ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Thu, 30 Nov 2023 19:46:39 GMT2023-11-30T19:46:39Z50531- Complex Raman amplitude recovery and dynamics from the Raman excitation profile: Application to iodobenzene and azulenehttps://scholarbank.nus.edu.sg/handle/10635/77418Title: Complex Raman amplitude recovery and dynamics from the Raman excitation profile: Application to iodobenzene and azulene
Authors: Feng, Z.W.; Lee, S.Y.
Abstract: Recovering the complex amplitude or phase from an intensity, which is given as the modulus square of the amplitude, is a problem common to diverse physical areas. The focus of this paper is on the Raman excitation profile - the Raman intensity of a mode as a function of the excitation energy - which is given by the modulus square of the Raman amplitude. Three methods, with different principles, are presented for amplitude or phase recovery: the dispersion or energy-frame method; the z-transform or time-frame method; and the maximum entropy method. A comparison function technique is introduced to address the usual situation where the measured intensity is band-limited. There are two classes of problems, minimum phase and non-minimum phase, and the mapping from the intensity to the complex amplitude may not be unique. The non-minimum phase situation occurs when the analytically extended complex amplitude, with the energy E replaced by ξ = γ - iE, has zeros in the right-half complex plane. These zeros have implications for the system dynamics. An algorithm is presented to search for the critical zeros. The characteristics of the zeros are studied with a two-mode harmonic model, and the theory is applied to the Raman excitation profiles of iodobenzene and azulene. © 2001 John Wiley & Sons, Ltd.
Mon, 01 Jan 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/774182001-01-01T00:00:00Z
- Simple results for Raman scatteringhttps://scholarbank.nus.edu.sg/handle/10635/94807Title: Simple results for Raman scattering
Authors: Lee, S.-Y.
Abstract: The time-dependent formulation of Raman scattering is used to derive simple expressions for Raman progressions and combination bands. A procedure to calculate the harmonic potential parameters in the Franck-Condon region and the homogeneous damping constant is presented. It is shown that all Raman bands can be evaluated by using a simple recursion relation if the short-time representation for the correlation function is adequate. A numerical application to the resonance Raman spectrum of Cs3[Re2OCl10] is described. © 1992.
Sun, 01 Mar 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/948071992-03-01T00:00:00Z
- Solid-phase combinatorial synthesis of benzothiazole and 2,3-dihydro-[1,5]-benzothiazepine derivativeshttps://scholarbank.nus.edu.sg/handle/10635/94832Title: Solid-phase combinatorial synthesis of benzothiazole and 2,3-dihydro-[1,5]-benzothiazepine derivatives
Authors: Lee, C.L.; Lam, Y.; Lee, S.-Y.
Abstract: Bis-(2-nitro-4-carboxyphenyl) disulfide was loaded on Wang resin and Rink amide resin. The nitro group was reduced to its amine with concomitant cleavage of the disulfide bond using SnCl2-2H2O to afford 2. Condensation of an aldehyde and nucleophilic attack on an α,β-unsaturated ketone, followed by TFA cleavage from the resin, gave benzothiazole 3 and 2,3-dihydro-[1,5]-benzothiazepine 4, respectively. © 2000 Elsevier Science Ltd.
Mon, 01 Jan 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/948322001-01-01T00:00:00Z
- A time-dependent wave packet study of the H 4 four-center reactionhttps://scholarbank.nus.edu.sg/handle/10635/93026Title: A time-dependent wave packet study of the H 4 four-center reaction
Authors: Lu, Y.; Zhang, D.H.; Lee, S.-Y.
Abstract: A quantum model based on the time-dependent initial state selected wave packet approach was developed to study the four-center (4C) reaction, A 2 + B 2 → 2AB, and the competing collision induced dissociation (CID), A 2 + B 2 → A + B 2 + A, as applied to the H 2(v 1) + H 2(v 2) system important in combustion. A reduced three-dimensional model of the reaction with the atoms constrained to an isosceles trapezium and a realistic global potential energy surface of Aguado et al. [J. Chem. Phys. 101 (1994) 2742], following Hernández and Clary [J. Chem. Phys. 104 (1996) 8413], was used. A method to analyse the reaction flux for 4C and CID reaction probabilities is presented. The initial A 2 vibrational excitation is not only more efficient than translational energy in facilitating the 4C and CID processes, it also reduces the threshold energy. Both the 4C and CID processes exhibit similar threshold energy behavior. For low vibrational excitation in the A 2 diatom, the 4C process is dominant; as the A 2 diatom becomes highly excited the CID process becomes more important at low collision energies with B 2, but as the collision energy increases the 4C process is favored again. © 2004 Elsevier B.V. All rights reserved.
Mon, 31 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/930262005-01-31T00:00:00Z
- A transform from absorption to Raman excitation profile. A time-dependent approachhttps://scholarbank.nus.edu.sg/handle/10635/93027Title: A transform from absorption to Raman excitation profile. A time-dependent approach
Authors: Lee, S.-Y.; Yeo, R.C.K.
Abstract: An alternative time-frame approach, which is canonically conjugate to the energy-frame approach, for implementing the transform relations for calculating Raman excitation profiles directly from the optical absorption spectrum is presented. Practical and efficient fast Fourier transformation in the time frame replaces the widely used Chan and Page algorithm for evaluating the Hilbert transform in the energy frame. The time-frame approach is applied to: (a) a two-mode model which illustrates the missing mode effect in both absorption and Raman excitation profiles, (b) carotene, in which both the absorption spectrum and the Raman excitation profile show vibrational structure and (c) hexamethylbenzene: TCNE electron donor-acceptor complex where the same spectra are structureless and the Raman excitation profile for the 168 cm-1 mode poses a problem for the energy-frame approach. A similar time-frame approach can be used for the inverse transform from the Raman excitation profile to the optical absorption spectrum. © 1994.
Fri, 29 Apr 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/930271994-04-29T00:00:00Z
- Ab Initio calculations on normal mode vibrations and The raman and IR spectra of the [B3O6]3- metaborate ringhttps://scholarbank.nus.edu.sg/handle/10635/93035Title: Ab Initio calculations on normal mode vibrations and The raman and IR spectra of the [B3O6]3- metaborate ring
Authors: Wu, K.; Lee, S.-Y.
Abstract: Normal vibrational modes of the [B3O6]3- metaborate ring are obtained at the Hartree-Fock level by ab initio calculations. The Raman and IR spectra are predicted, and the former are compared with available experimental results of molten crystal metaborates that contain [B3O6]3- rings, i.e., β-BaB2O4 and CsBO2 crystals. The internal vibrations of the [B3O6]3- ring are dominant in the whole crystal lattice vibrations of these nonlinear optical crystals. Also, the [B3O6]3- ring accounts for the IR transparency cut-off in such crystals. It is deduced from the predicted IR spectrum of a [B3O6]3- ring that the transparency cut-off frequency of the β-BaB2O4 crystal on the IR side is below 4000 cm-1 (>2.5 μm), which agrees well with the measured data. This study is also useful for understanding the vibrational contributions to nonlinear optical polarizabilities.
Thu, 30 Jan 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/930351997-01-30T00:00:00Z
- Ab initio potential-energy surfaces for the reactions OH+H2↔H2O+Hhttps://scholarbank.nus.edu.sg/handle/10635/93037Title: Ab initio potential-energy surfaces for the reactions OH+H2↔H2O+H
Authors: Yang, M.; Zhang, D.H.; Collins, M.A.; Lee, S.-Y.
Abstract: The potential energy surfaces (PES) for the reactions of the hydroxyl group with the hydrogen molecule and the competing exchange processes were analyzed. The ground state PES was constructed from a hybrid of a number of ab initio estimates of the electronic energy. It was found that the reaction dynamics for the collisions of OH and H2 do not take place on the single adiabatic ground state surface due to the presence of another low lying state in the entrance channel.
Sun, 01 Jul 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/930372001-07-01T00:00:00Z
- Accuracy of the centrifugal sudden approximation in the H+H2O reaction and accurate integral cross sections for the H+H2O→H2+OH abstraction reactionhttps://scholarbank.nus.edu.sg/handle/10635/93042Title: Accuracy of the centrifugal sudden approximation in the H+H2O reaction and accurate integral cross sections for the H+H2O→H2+OH abstraction reaction
Authors: Zhang, D.H.; Yang, M.; Lee, S.-Y.
Abstract: The time-dependent wave packet method was used to test the accuracy of the CS approximation for the H + H2O reaction, and to calculate the integral cross section for the abstraction reaction. The total abstraction and exchange probabilities for J=15 were calculated by including 2 K-blocks and treating both OH bonds in the H2O reagent reactively. Overall, significant results were obtained.
Sun, 08 Dec 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/930422002-12-08T00:00:00Z
- A seven-dimensional quantum study of the H+CH4 reactionhttps://scholarbank.nus.edu.sg/handle/10635/93000Title: A seven-dimensional quantum study of the H+CH4 reaction
Authors: Yang, M.; Zhang, D.H.; Lee, S.-Y.
Abstract: A reaction between H and CH4 was studied by the initial state-selected time-dependent wave packet method. The CH bond lengths in the nonreacting CH3 group were fixed. This was done to reduce the number of degrees of freedom to seven. The rate constant for the ground rovibrational initial state was compared with the experimental and theoritical results. The fundamental vibrational excitations of CH4 were studied for the effects on the reaction. It was found that while studying the reaction, it was important to deal with the umbrella motion of the CH3 group.
Sun, 01 Dec 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/930002002-12-01T00:00:00Z
- An embedded cluster study of dimer buckling on the Si(100) surfacehttps://scholarbank.nus.edu.sg/handle/10635/93085Title: An embedded cluster study of dimer buckling on the Si(100) surface
Authors: Yang, C.; Lee, S.Y.; Kang, H.C.
Abstract: Both Si9H12 and Si15H16 cluster models for the Si(100) surface were studied using the Hartree-Fock molecular-orbital method and density functional theory. Our investigation shows that the ground state of the Si(100) surface consists of buckled dimers, contrary to the results of a number of previous embedded cluster calculations, but in agreement with some recent slab calculations. The relaxation constraints used in previous embedded cluster studies probably do not model the relaxation of the Si(100) surface layers adequately. © 1997 American Institute of Physics.
Fri, 22 Aug 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/930851997-08-22T00:00:00Z
- Theory of femtosecond stimulated Raman spectroscopyhttps://scholarbank.nus.edu.sg/handle/10635/77261Title: Theory of femtosecond stimulated Raman spectroscopy
Authors: Lee, S.-Y.; Zhang, D.; McCamant, D.W.; Kukura, P.; Mathies, R.A.
Abstract: Femtosecond broadband stimulated Raman spectroscopy (FSRS), a technique that produces high-resolution vibrational spectra from either the ground or excited electronic states of molecules, free from background fluorescence, was analyzed. A narrow bandwidth ∼1-3 ps Raman pump pulse with a continuum ∼30-50 fs Stokes probe pulse to produce sharp Raman gains was simultaneously used by FSRS. It was shown that when FSRS is preceded by a femtosecond actinic pump pulse that initiates the photochemistry of interest, time-resolved Raman spectroscopy can be carried out. Extension of the quantum-mechanical description to the case where the Raman pump beam is on resonance with an excited electronic state, was also discussed.
Sun, 22 Aug 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/772612004-08-22T00:00:00Z
- Transition state wave packet study of hydrogen diffusion on Cu(100) surfacehttps://scholarbank.nus.edu.sg/handle/10635/77310Title: Transition state wave packet study of hydrogen diffusion on Cu(100) surface
Authors: Zhang, D.H.; Light, J.C.; Lee, S.-Y.
Abstract: The transition state wave packet (TSWP) approach to the thermal rate constant based on the flux-flux autocorrelation function is used to investigate the diffusion dynamics of an H atom on the Cu(100) surface in the uncorrelated hopping regime. The high efficiency of the approach makes it feasible to include up to eight Cu modes explicitly in the time dependent quantum simulation. This is necessary since on the rigid surface the flux-flux autocorrelation function never decays to a negligibly small value to give a converged rate constant. For short times, the Cu modes included dynamically merely have a zero-point-energy effect on the flux-flux autocorrelation function. For longer times, however, the Cu modes absorb the activation energy of the H atom and effectively suppress recrossing of the transition state surface, resulting in convergence of the autocorrelation function and the hopping rate. For this system, recrossing of the transition state surface is minimal with the medium damping present, and the converged hopping rate can be well approximated by the short time behavior of the correlation function on the rigid surface. In addition, we find that the contributions of the excited Cu modes to the hopping rate may be accurately modeled by thermal "transition state" factors. Based on this, a new quantum transition state theory (QTST) is derived. The new theory provides a general way to calculate the approximate quantum correction to the traditional TST. It also provides a systematic and flexible tool to calculate the rate constant at any desired level of accuracy between the traditional TST level and the exact result. Finally, since the surface relaxation due to the presence of the H atom lowers both the energies of H atom in the binding well and on the saddle point almost equally, it only minimally affects the hopping rate, provided the configuration of the surface atoms is fully relaxed initially. © 1999 American Institute of Physics.
Fri, 01 Oct 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/773101999-10-01T00:00:00Z
- Time frame viewpoint of resonance Raman enhancement of a non-totally symmetric vibrationhttps://scholarbank.nus.edu.sg/handle/10635/77292Title: Time frame viewpoint of resonance Raman enhancement of a non-totally symmetric vibration
Authors: Lee, S.-Y.
Abstract: The time frame approach is presented to describe the resonance Raman enhancement of a non-totally symmetric vibration due to vibronic coupling between two nearby electronic states. It is shown that in contrast to the resonance Raman enhancement of a totally symmetric vibration, the resonant contribution to the Raman scattering tensor for a non-totally symmetric vibration arises from the electronic state that is vibronically coupled to the electronic state first reached by the incident light. The second-order differencing method of Kosloff is used to numerically solve the coupled time-dependent Schrödinger equation in an application to pyrazine. In the case where the vibronically coupled states have the same oscillator frequency, it is shown that a unitary transformation of the wave packets leads to an immediate picture of the adiabatic states, as well as provide a qualitative explanation of various factors on the Raman intensity. © 1990 American Institute of Physics.
Mon, 01 Jan 1990 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/772921990-01-01T00:00:00Z
- Theory of Raman scattering with pulses: Application to continuum Raman spectroscopyhttps://scholarbank.nus.edu.sg/handle/10635/77263Title: Theory of Raman scattering with pulses: Application to continuum Raman spectroscopy
Authors: Lu, J.; Lee, S.-Y.
Abstract: A theory of real-time dependence of Raman scattering for a pulse-mode laser is developed within second-order perturbation theory and using the wavepacket terminology. The rate of spontaneous Raman emission with a pulse correctly reduces to the dynamical equivalent of the Kramers-Heisenberg-Dirac expression in the monochromatic limit. We apply the theory to continuum Raman scattering for short and long pulses and varying pulse carrier frequency. The rate of Raman emission as a function of time and pulse carrier frequency, from an initial ground vibrational state to various final vibrational states, is shown to be structureless for all pulses, and for pulses that are longer than the dissociation time the rate also rises and decays with the pulses. This is contrary to recent reports of recurring resonance fluorescence-type structures at long times after the pulse has vanished. We explain why such structures are unphysical for continuum Raman scattering. Results are also presented for excitation from an initial first excited vibrational state. © 1996 American Institute of Physics.
Sat, 01 Jun 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/772631996-06-01T00:00:00Z
- Theory of multidimensional wavepacket propagationhttps://scholarbank.nus.edu.sg/handle/10635/77262Title: Theory of multidimensional wavepacket propagation
Authors: Lee, S.-Y.
Abstract: Ehrenfest's theorem implies that a gaussian remains a gaussian when propagated in a general (time-dependent and multidimensional) harmonic potential. We shall prove that the statement remains true with the replacement of a gaussian with a harmonic oscillator. For the one-dimensional case, this is implicit in the work of Meyer. Here, we prove it more generally for the multidimensional case. A complete, orthonormal, evolving basis of harmonic oscillator wavefunctions can then be constructed by using a local, time-dependent, harmonic approximation to the potential. An evolving wavepacket in the actual potential can be expanded in the basis set, and the coefficients of the expansion obey a set of coupled, linear, first-order differential equations. The theory has practical applications for processes such as Raman scattering, photodissociation, and other time-dependent processes that can benefit from multidimensional wavepacket propagation. © 1986.
Wed, 15 Oct 1986 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/772621986-10-15T00:00:00Z
- Solid phase synthesis of pyridazine derivatives using polymer-bound sodium benzenesulfinatehttps://scholarbank.nus.edu.sg/handle/10635/77005Title: Solid phase synthesis of pyridazine derivatives using polymer-bound sodium benzenesulfinate
Authors: Chen, Y.; Lam, Y.; Lee, S.-Y.
Abstract: A new solid phase synthesis of 3,6-disubstituted pyridazine derivatives, resulting from the reaction of polymer-bound sodium benzenesulfinate with α-bromoketone substrates followed by condensation with hydrazine, is described. Mild basic conditions for the condensation reaction simultaneously release the desired product from the solid support. The crystal structure of 3,6-bis(p-chlorophenyl)pyridazine is reported.
Mon, 01 Jan 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/770052001-01-01T00:00:00Z
- Solid-phase combinatorial synthesis of 1,4-benzoxazin-3(4H)-one and 1,4-benzothiazin-3(4H)-one derivativeshttps://scholarbank.nus.edu.sg/handle/10635/77007Title: Solid-phase combinatorial synthesis of 1,4-benzoxazin-3(4H)-one and 1,4-benzothiazin-3(4H)-one derivatives
Authors: Lee, C.L.; Chan, K.P.; Lam, Y.; Lee, S.Y.
Abstract: The first solid-phase synthesis of 1,4-benzothiazin-3(4H)-ones and 1,4-benzoxazin-3(4H)-ones is reported. Alkylation of the immobilized 4-hydroxy-3-nitrobenzamide (2a) and 3-nitro-4-sulfanylbenzamide (2b), followed by reduction and cyclization gave 4. Further alkylation and acylation in the presence of sodium hydride followed by TFA cleavage gave the desired 1,4-benzothiazin-3(4H)-ones and 1,4-benzoxazin-3(4H)-ones. © 2001 Elsevier Science Ltd.
Mon, 05 Feb 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/770072001-02-05T00:00:00Z
- Spectral moment method versus least-squares Franck-Condon analysis for vibrationally resolved absorption spectrahttps://scholarbank.nus.edu.sg/handle/10635/77037Title: Spectral moment method versus least-squares Franck-Condon analysis for vibrationally resolved absorption spectra
Authors: Lee, S.-Y.; Lee, S.C.
Abstract: An accurate, back-of-the-envelope spectral moment method is described to obtain molecular parameters of excited state molecules and ions from vibrationally resolved absorption spectra. Since it is not an iterative procedure, the spectral moment method is clearly much faster than the least-squares Franck-Condon analysis for obtaining molecular parameters, and the procedure described here can even be implemented on a hand-held calculator. Some of the drawbacks of Franck-Condon analysis are overcome by the spectral moment method. Comparison of molecular parameters for a diverse range of excited state molecules and ions obtained by the spectral moment method versus Franck-Condon analysis or rotational spectroscopy reveal the high accuracy of the procedure here. Simulations of vibrationally resolved absorption spectra show that the spectral moment method with the Morse potential approximation gives an envelope that matches very well the observed spectra. © 1991 American Institute of Physics.
Tue, 01 Jan 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/770371991-01-01T00:00:00Z
- State-to-state integral cross section for the H + H2O → H2 + OH abstraction reactionhttps://scholarbank.nus.edu.sg/handle/10635/94868Title: State-to-state integral cross section for the H + H2O → H2 + OH abstraction reaction
Authors: Zhang, D.H.; Xie, D.; Yang, M.; Lee, S.-Y.
Abstract: An overview is given on the first five dimensional (5D) state-to-state integral cross sections (ICS) for the H + H2O → H2(v1,j1)+OH(j2) reaction for the initial ground vibrational state. Since three of the four atoms are hydrogens, the system is an ideal candidate for pursuing both high quality ab initio calculation of a potential energy surface (PES) and accurate quantum reactive scattering calculations.
Tue, 31 Dec 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/948682002-12-31T00:00:00Z
- Classical theory for real-time femtosecond probing of the NaI* photodissociationhttps://scholarbank.nus.edu.sg/handle/10635/93312Title: Classical theory for real-time femtosecond probing of the NaI* photodissociation
Authors: Lee, S.-Y.; Pollard, W.T.; Mathies, R.A.
Abstract: Femtosecond pump-probe experiments [Rosker et al., Chem. Phys. Lett. 146, 175 (1988)] on the dissociation of NaI* are modelled classically to obtain the absorption transients as a function of the pump and probe wavelengths. The initial ground state, the optically pumped predissociating state, and the third surface that is coupled by the probe pulse are explicitly included. The classical model can almost quantitatively explain all the features of the experimental results. The oscillations in the transients are shown to be due to molecules trapped in the adiabatic well, with most of the intensity coming from the covalent region of the well before the crossing point rx. The rising troughs in the transients are due to successive leaks out of the well into the covalent region after the crossing point rx, leading to dissociation. The difference in the absorption transient between on-resonance 589 nm probing as compared to off-resonance 612 nm and 580 nm probing is shown to arise from the difference in Lorentzian absorption widths between the trapped (500 cm-1) and dissociating (100 cm-1) covalent molecules, with the transition dipole moment to the third surface having about the same magnitude over the range of the covalent potential. © 1989 American Institute of Physics.
Sun, 01 Jan 1989 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/933121989-01-01T00:00:00Z
- Branching ratio in the HD+OH reaction: A full-dimensional quantum dynamics study on a new ab initio potential energy surfacehttps://scholarbank.nus.edu.sg/handle/10635/93213Title: Branching ratio in the HD+OH reaction: A full-dimensional quantum dynamics study on a new ab initio potential energy surface
Authors: Zhang, D.H.; Yang, M.; Lee, S.-Y.
Abstract: The title reaction on the YZCL2 potential energy surface (PES) was studied using a full-dimensional quantum dynamics. The branching ratio in the HD+OH reaction was determined and it was found that the rotational excitation of the HD reagent increased the rate coefficient for forming the H2O+D product. For an integral cross section, thermal rate coefficients and their corresponding branching ratios, theoretical results were compared with available experimental data. Agreement between theory and experiment was revealed for branching ratio of thermal rate coefficients.
Tue, 22 May 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/932132001-05-22T00:00:00Z
- Quantum rate constants for the H2+OH reaction with the centrifugal sudden approximationhttps://scholarbank.nus.edu.sg/handle/10635/94645Title: Quantum rate constants for the H2+OH reaction with the centrifugal sudden approximation
Authors: Zhang, D.H.; Light, J.C.; Lee, S.-Y.
Abstract: The cumulative reaction probability (CRP) has been calculated for the H2+OH↔H2O+H in its full dimensionality by using the centrifugal sudden (CS) approximation for J>0. The Boltzmann average of the CRP provides the most accurate thermal rate constant to date for the title reaction on the Walch, Dunning, Schatz, Elgersma (WDSE) potential energy surface (PES). It is found that the theoretical rate is larger than the experimental value in the low temperature region (a factor of ∼1.8 at 300 K), and smaller than the experimental value for temperatures higher than 500 K, indicating that a more accurate PES is needed to provide a quantitative description of the title reaction. We also demonstrate that the "J-shifting" approximation in which we calculate N(J>K,K) from N(J=K,K) by an energy shift works very well for this reaction. However, the "J- and K-shifting" approximation [calculating N(J,K) from N(J=0,K=0)] overestimates the rate for this reaction by about 60% for all the temperatures investigated. It is also found that the CS rate constant is substantially lower than the rate constant for the ground rovibrational state of the reagents calculated on the same PES, indicating that initial rotational excitation is important to the thermal rate constant for this reaction (it causes a decrease). © 1998 American Institute of Physics.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/946451998-01-01T00:00:00Z
- Quantum mechanical integral cross sections and rate constants for the F+HD reactionshttps://scholarbank.nus.edu.sg/handle/10635/76845Title: Quantum mechanical integral cross sections and rate constants for the F+HD reactions
Authors: Zhang, D.H.; Lee, S.-Y.; Baer, M.
Abstract: The temperature-dependent rate constants for two possible products of the (F+HD) system were studied via quantum mechanics calculation. To obtain the rate constants, the energy-dependent rotational-state-selected cross sections were calculated for the Stark-Werner and the Hartke-Stark-Werner potential energy surfaces. The two potential energy surfaces yielded different rate constants for both products.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/768452000-01-01T00:00:00Z
- Quasi-classical models of transition state absorption or emissionhttps://scholarbank.nus.edu.sg/handle/10635/76847Title: Quasi-classical models of transition state absorption or emission
Authors: Lee, S.-Y.; Pollard, W.T.; Mathies, R.A.
Abstract: By making a short-time approximation to the correlation function in the quantum result for transition state absorption (or emission) we obtain the Lorentzian and reflection results as integrals of simple configuration space functions. These and the time-integrated quantum results are used to derive and unify the following descriptions of transition-state absorption: (a) the classical model of Bersohn and Zewail, (b) the time-dependent wave mechanical description by Agrawal, Mohan and Sathyamurthy, (c) the classical trajectory approach by Polanyi and coworkers and (d) the time-independent quantum-mechanical description by Engel, Bacic, Schinke and Shapiro. © 1989.
Fri, 03 Nov 1989 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/768471989-11-03T00:00:00Z
- Quantum theory for transition state absorptionhttps://scholarbank.nus.edu.sg/handle/10635/76846Title: Quantum theory for transition state absorption
Authors: Lee, S.-Y.; Pollard, W.T.; Mathies, R.A.
Abstract: A time-dependent quantum model involving two wave packets on two excited-state surfaces is presented to describe absorption (or emission) from the transition state of a chemical reaction. The connection between the quantum result and existing classical theories is shown. The model ia applied to the direct dissociation of ICN* and gives results in good agreement with experiment. The dissociation time - the time to half-maximal absorption - is almost invariant with the pulse width but is dependent on the probe wavelength. A lower absorption plateau and a longer dissociation time is predicted for probe energies above the asymptotic resonance energy. © 1989.
Fri, 25 Aug 1989 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/768461989-08-25T00:00:00Z
- Quantum dynamics of the D2 + OH reactionhttps://scholarbank.nus.edu.sg/handle/10635/94642Title: Quantum dynamics of the D2 + OH reaction
Authors: Zhang, D.H.; Yang, M.; Lee, S.-Y.
Abstract: A quantum dynamics study of the D2 + OH reaction was presented by using the initial state selected time-dependent wave packet method on the YZCL2 potential energy surface. Integral cross sections for a number of rotationally excited states were reported. The investigation of the influence of the reagent rotation on the dynamics and the dependence of cross sections on K0, which was the projection of reagent rotation on the body-fixed z axis, was done.
Fri, 08 Feb 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/946422002-02-08T00:00:00Z
- Quantum dynamics on new potential energy surfaces for the H2+OH→H2O+H reactionhttps://scholarbank.nus.edu.sg/handle/10635/94643Title: Quantum dynamics on new potential energy surfaces for the H2+OH→H2O+H reaction
Authors: Yang, M.; Zhang, D.H.; Collins, M.A.; Lee, S.-Y.
Abstract: For the H2+OH reaction, quantum dynamics on two interpolated potential energy surfaces (PES) was studied. The first PES was based on MRCI/aug-cc-pVTZ and QCISD(T)/6-311++G(3df,2pd) ab initio calculations. In the second one, the energies at the interpolation data points were improved to UCCSD(T)/aug-cc-pVQZ level. This level of ab initio calculations produced good agreement between theory and experiment for thermal rate coefficient for temperatures upto 1050 K.
Thu, 15 Mar 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/946432001-03-15T00:00:00Z
- Probing the transition state via photoelectron and photodetachment spectroscopy of H3O-https://scholarbank.nus.edu.sg/handle/10635/94620Title: Probing the transition state via photoelectron and photodetachment spectroscopy of H3O-
Authors: Zhang, D.H.; Yang, M.; Collins, M.A.; Lee, S.-Y.
Abstract: The H3O- anion has stable and metastable structures that resemble configurations in the vicinity of the transition state for the neutral reactions OH + H2 ↔ H2O + H. Photoelectron spectroscopy of this anion probes the neutral reaction dynamics in the critical transition-state region. Accurate quantum dynamics calculations of the photoelectron intensity and photodissociation product energies are shown to provide a quantitatively reliable means of interpreting such experimental observations and reveal a detailed picture of the reaction dynamics.
Tue, 03 Sep 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/946202002-09-03T00:00:00Z
- Phase recovery from the raman excitation profile, time domain information and transform theoryhttps://scholarbank.nus.edu.sg/handle/10635/76741Title: Phase recovery from the raman excitation profile, time domain information and transform theory
Authors: Lee, S.-Y.; Feng, Z.W.; Yeo, R.C.K.
Abstract: The phase recovery from the vibrational Raman excitation profile (REP), which contains only the modulus of the Raman amplitude, is discussed for the general situation where the Raman amplitude, with excitation energy extended in the complex plane, may have zeros in the right-half plane. The focus is on the dispersion method, with all results derived by contour integration. The new results for phase recovery, however, apply to both the dispersion and maximum entropy methods. An iterative procedure, with rapid convergence, is presented to overcome the experimental REP data being given in a limited energy range. The forward transform from the electronic absorption spectrum (ABS) to the REP and the inverse transform from the REP to the ABS are presented in a unified manner. The ubiquitous Hubert transform is shown to be readily evaluated by the fast Fourier transform algorithm. Calculations are presented for β-carotene, a two-mode harmonic model with diffuse vibrational structure, azulene and iodobenzene to illustrate the theory. © 1997 by John Wiley & Sons, Ltd.
Wed, 01 Jan 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/767411997-01-01T00:00:00Z
- Phase recovery and reconstruction of the Raman amplitude from the Raman excitation profilehttps://scholarbank.nus.edu.sg/handle/10635/76740Title: Phase recovery and reconstruction of the Raman amplitude from the Raman excitation profile
Authors: Lee, S.-Y.
Abstract: The phase recovery from the Raman excitation profile and the reconstruction of the Raman amplitude is solved for the general situation where the Raman amplitude, when extended in the complex plane, may have zeros in the right-half plane. New results for phase recovery are derived for the dispersion method by contour integration, which extends the usual minimum phase problem to the non-minimum phase case. An iterative procedure, with rapid convergence, is presented to overcome the problem of the experimental Raman excitation profile being given in a limited energy range. Calculations are presented for azulene and iodobenzene to illustrate the theory. © 1995.
Fri, 10 Nov 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/767401995-11-10T00:00:00Z
- Potential energy surfaces and effects on electronic and Raman spectrahttps://scholarbank.nus.edu.sg/handle/10635/76793Title: Potential energy surfaces and effects on electronic and Raman spectra
Authors: Lee, S.-Y.
Tue, 01 Jan 1985 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/767931985-01-01T00:00:00Z
- Effects of reagent rotation on the dynamics of the H2+OH reaction: A full dimension quantum studyhttps://scholarbank.nus.edu.sg/handle/10635/93668Title: Effects of reagent rotation on the dynamics of the H2+OH reaction: A full dimension quantum study
Authors: Zhang, D.H.; Lee, S.-Y.
Abstract: We have extended the time-dependent wave packet method to calculate cross sections and rate constants for rotationally excited initial states by using the centrifugal sudden (CS) approximation. A detailed study of the effects of rotational excitation of reagents on the title reaction on the WDSE PES has been carried out. It is found that (a) OH rotational excitation very mildly enhances the total cross section, (b) H2 rotational excitation quite substantially reduce the cross section, and (c) simultaneous OH and H2 rotational excitation has a largely uncorrelated effect. As a result, we found that the thermal rate constant can be obtained fairly accurately by only taking into account the effect of H2 rotation. A model calculation by changing the mass of an O atom reveals that the weak dependence of the cross section on OH rotation is not because the O atom is left relatively stationary by OH rotation. We speculate that it may be a general feature for the diatom-diatom reaction that the nonreactive diatom acts as a spectator not only vibrationally but also rotationally. It was also found that the "J-shifting" approximation works quite well for the reaction. On the other hand, the effect of K on the dynamics is found to be much stronger and more complicated than the J effect, making the "K-shifting" approximation not good for the reaction. © 1998 American Institute of Physics.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/936681998-01-01T00:00:00Z
- Effects of reagent rotation and the accuracy of the centrifugal sudden approximation in the H2+CN reactionhttps://scholarbank.nus.edu.sg/handle/10635/93667Title: Effects of reagent rotation and the accuracy of the centrifugal sudden approximation in the H2+CN reaction
Authors: Zhang, D.H.; Lee, S.-Y.
Abstract: This paper presents fully converged integral cross sections for the ground rovibrational state and some rotationally excited initial states for the title reaction on the TSH3 PES. The initial state selected time-dependent wave packet method has been employed in the calculation with all important K blocks in the body-fixed (BF) frame included. We find that CN rotational excitation up to j2 = 7 essentially has no effect on the integral cross section, while H2 rotational excitation substantially reduces the cross section. As a result, the thermal rate constant can be obtained accurately by only taking into account the effect of H2 rotational excitation. It is found that the resulting thermal rate constant is considerably smaller than the initial state selected rate constant for the ground rovibrational state. It is also smaller than the experimental rate constant by a factor of 3 and 30% at T = 209 K and 447 K, respectively, indicating the TSH3 PES used in the calculation is not quantitatively accurate in describing the reaction. In addition, we examine in detail the accuracy of the centrifugal sudden (CS) approximation to the reaction. Comparison between this reaction and the H2+OH reaction is also carried out when possible. © 2000 American Institute of Physics.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/936672000-01-01T00:00:00Z
- Fully converged integral cross sections of diatom-diatom reactions and the accuracy of the centrifugal sudden approximation in the H2+OH reactionhttps://scholarbank.nus.edu.sg/handle/10635/93867Title: Fully converged integral cross sections of diatom-diatom reactions and the accuracy of the centrifugal sudden approximation in the H2+OH reaction
Authors: Zhang, D.H.; Lee, S.-Y.
Abstract: The initial state selected time-dependent wave packet method has been extended to calculate integral cross sections for diatom-diatom chemical reactions without the CS (centrifugal sudden) approximation by including all important K (the projection of the total angular momentum on the body-fixed axis) blocks in the body-fixed frame. We report the first fully converged cross section for the ground rovibrational state of the title reaction and present a detail study of the accuracy of the CS approximation to the reaction. We find that for the ground rovibrational state the CS approximation works very well, but its accuracy deteriorates with increasing reagent rotational excitation. As expected, and as found in atom-diatom reactions, the CS approximation works much better in high energy region than in low energy region. In low energy region, the coupled channel cross sections are larger than the CS ones for all the rotationally excited states investigated here, in particular for the highly excited states. It is found the CS approximation gives rise to about 10% error in H2 or OH rotationally averaged rate constant. If simultaneous OH and H2 rotational excitation does not have a correlated effect on dynamics, the CS approximation introduces about 19% error in thermal rate constant for the reaction for low temperatures which is considerably larger than what is expected of a few percent. © 1999 American Institute of Physics.
Mon, 01 Mar 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/938671999-03-01T00:00:00Z
- A theoretical distinction between time-resolved resonance Raman and resonance fluorescencehttps://scholarbank.nus.edu.sg/handle/10635/75496Title: A theoretical distinction between time-resolved resonance Raman and resonance fluorescence
Authors: Lu, J.; Du, S.-D.; Fan, K.-N.; Lee, S.-Y.
Abstract: Based on the time-dependent theory, an analysis of the distinction between resonance Raman (RR) and resonance fluorescence (RF) with pulse excitation was presented. The real population of the intermediate state gives two optical components - the independent time evolution of intermediate ket and bra states generates RR while RF originates from the phase coherent between ket and bra states. In cw limit, the transition probability of spontaneous emission with pulse excitation can be reduced to the classical theory.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/754962000-01-01T00:00:00Z
- A rapid method for determining excited state surface parameters and bond length in diatomic molecules and calculating wavefunctions for Franck-Condon factors using the quantum momentum methodhttps://scholarbank.nus.edu.sg/handle/10635/75478Title: A rapid method for determining excited state surface parameters and bond length in diatomic molecules and calculating wavefunctions for Franck-Condon factors using the quantum momentum method
Authors: Lee, S.C.; Lee, S.-Y.
Abstract: A fast and simple method for determining molecular potential energy parameters for excited dectronic states is presented. This method uses the moments of the observed vibronic spectra. It is particularly accurate in determining equilibrium bond lengths and is a good substitute for an iterative, least-squares Franck-Condon analysis. The calculation of wavefunctions for Franck-Condon factors Using the quantum momentum method is also reported. This method is not limited to low vibrational numbers and does not have problems with overflow and insufficient precision that are associated with methods using analytic forms of the Morse potential wavefunction. A program incorporating both the spectral moment method and the quantum momentum method is described. It provides a package for evaluating excited state molecular potential parameters and for simulating electronic-vibrational spectra for one vibrational mode at a time. © 1991.
Tue, 01 Jan 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/754781991-01-01T00:00:00Z
- A simple method to determine bond lengths and excited state surfaces from electronic-vibrational spectrahttps://scholarbank.nus.edu.sg/handle/10635/75486Title: A simple method to determine bond lengths and excited state surfaces from electronic-vibrational spectra
Authors: Lee, S.-Y.; Lai, C.-H.
Abstract: A fast and efficient method using the spectral moments of an electronic-vibrational spectrum is described to determine the harmonic and Morse potential fits to the excited state potential in the Franck-Condon region. Some of the drawbacks of the Franck-Condon least-squares fitting procedure are overcome by the moment method. The method is applied to some diatomics of current interest, spanning a wide range of bond length change in the electronic transition. The accuracy of the results suggests that the spectral moment method can be a replacement for the traditional and still popular Franck-Condon analysis. © 1990.
Fri, 23 Mar 1990 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/754861990-03-23T00:00:00Z
- First-principles theory for the H + H2O, D2O reactionshttps://scholarbank.nus.edu.sg/handle/10635/93819Title: First-principles theory for the H + H2O, D2O reactions
Authors: Zhang, D.H.; Collins, M.A.; Lee, S.-Y.
Abstract: A full quantum dynamical study of the reactions of a hydrogen atom with water, on an accurate ab initio potential energy surface, is reported. The theoretical results are compared with available experimental data for the exchange and abstraction reactions in H + D2O and H + H2O. Clear agreement between theory and experiment is revealed for available thermal rate coefficients and the effects of vibrational excitation of the reactants. The excellent agreement between experiment and theory on integral cross sections for the exchange reaction is unprecedented beyond atom-diatom reactions. However, the experimental cross sections for abstraction are larger than the theoretical values by more than a factor of 10. Further experiments are required to resolve this.
Fri, 03 Nov 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/938192000-11-03T00:00:00Z
- Breakdown of the spectator model for the OH bonds in studying the H + H2O reactionhttps://scholarbank.nus.edu.sg/handle/10635/93214Title: Breakdown of the spectator model for the OH bonds in studying the H + H2O reaction
Authors: Zhang, D.H.; Yang, M.; Lee, S.Y.
Abstract: The six-dimensional quantum dynamics study of the H+H2O reaction was reported by treating both OH bonds in the H2O reactant as reactive bonds. It was found that OH bond in the H2O reactant should be treated as reactive bonds to accurately investigate the exchange process. The results showed that the motion of one OH bond can be expanded by using a few vibrational basis functions.
Mon, 02 Sep 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/932142002-09-02T00:00:00Z
- Determination of excited-state potential energy surfaces in the Franck-Condon region from electronic absorption spectrahttps://scholarbank.nus.edu.sg/handle/10635/75892Title: Determination of excited-state potential energy surfaces in the Franck-Condon region from electronic absorption spectra
Authors: Lee, S.-Y.
Abstract: A fast and efficient method using the first and second moments of the electronic absorption spectrum is described to determine the harmonic fit to the excited-state potential about the ground-state equilibrium configuration, i.e., the Franck-Condon region. It is an improvement over the conventional harmonic Franck-Condon analysis in the following ways. (a) It uses the minimum information to determine the harmonic fit to the excited-state potential in the Franck-Condon region. (b) It is easy to use, since it is not a fitting procedure. (c) It gives a definite sign to the shift in bond length. (d) It provides one bound to the actual shift in bond length. (e) It is computationally more efficient and gives accurate results. Examples of some diatomics and a polyatomic with separable modes are given to illustrate the method. © 1990 American Chemical Society.
Mon, 01 Jan 1990 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/758921990-01-01T00:00:00Z
- Derivation of the reflection principle in continuum resonance Raman scatteringhttps://scholarbank.nus.edu.sg/handle/10635/75863Title: Derivation of the reflection principle in continuum resonance Raman scattering
Authors: Lee, S.-Y.
Abstract: We prove the reflection principle in continuum resonance Raman scattering as stated recently by Kolba, Manz, Schreier and Trisca. For a Stokes (or anti-Stokes) transition, the nodal pattern of the coordinate or momentum representation of the initial wavefunction |i> (or final wavefunction |f>) is mapped on the time-dependent overlap |<f;|i(t)>|. An interesting aspect of the proof is the use of all three approaches to Raman scattering: the Kramers-Heisenberg-Dirac sum-over-states approach, the Lee-Heller time-dependent approach, and the Hizhnyakov-Tehver transform method. We also derive new expressions for the resonance Raman scattering amplitude and associated correlation function in terms of the Rayleigh scattering amplitude and associated autocorrelation function. A new algorithm using a fast Fourier transform to implement the Hizhnyakov-Tehver transform method for fundamental Raman excitation profiles is also discussed. © 1993.
Fri, 19 Feb 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/758631993-02-19T00:00:00Z
- Continuous configuration time-dependent self-consistent field method for polyatomic quantum dynamical problemshttps://scholarbank.nus.edu.sg/handle/10635/75810Title: Continuous configuration time-dependent self-consistent field method for polyatomic quantum dynamical problems
Authors: Zhang, D.H.; Bao, W.; Yang, M.; Lee, S.-Y.
Abstract: A new continuous configuration time-dependent self-consistent field method has been developed to study polyatomic dynamical problems by using the discrete variable representation for the reaction system, and applied to a reaction system coupled to a bath. The method is very efficient because the equations involved are as simple as those in the traditional single configuration approach, and can account for the correlations between the reaction system and bath modes rather well.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/758102005-01-01T00:00:00Z
- Time-dependent wave packet study of the O + O2 (v = 0, j = 0) exchange reactionhttps://scholarbank.nus.edu.sg/handle/10635/95319Title: Time-dependent wave packet study of the O + O2 (v = 0, j = 0) exchange reaction
Authors: Yeh, K.-L.; Xie, D.; Zhang, D.H.; Lee, S.-Y.; Schinke, R.
Abstract: Time-dependent wave packet calculations were carried out to study the O + O2 (v = 0, j = 0) exchange reaction on the Siebert-Schinke-Bitterova potential energy surface. Because of the presence of a deep well supporting quasistable ozone complexes, it is found that one needs to propagate wave packets up to 20 ps of time to fully converge the pronounced resonance structures in the total reaction probabilities. We calculated the total reaction probability for total angular momentum J = 0 for collision energies up to 0.6 eV, and the integral cross section for collision energies up to 0.4 eV under the centrifugal-sudden approximation. To assess the accuracy of the CS approximation for the reaction, we calculated fully converged cross sections up to a collision energy of 0.04 eV. It is found that (a) both fully converged and centrifugal-sudden cross sections are full of a resonance structure, although not as pronounced as for the J = 0 reaction probability, and (b) the centrifugal-sudden approximation can only be used to accurately calculate the thermal rate constant for the reaction, but not the integral cross section.
Thu, 18 Sep 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/953192003-09-18T00:00:00Z
- Time-dependent Hartree approximation applied to the photodissociation of ICNhttps://scholarbank.nus.edu.sg/handle/10635/95318Title: Time-dependent Hartree approximation applied to the photodissociation of ICN
Authors: Lee, S.-Y.
Abstract: A time-dependent, quantum-mechanical calculation of wave packet dynamics in the Hartree approximation is applied to the nonadiabatic transition between the linear and bent excited state surfaces in ICN. The model of ICN photodissociation in the Ã continuum given by Goldfield et al. is used. Both the probability and the energy of the propagated Hartree wave packets are conserved. Starting with the ground wave packet on the linear excited state surface, there is a final transfer of about 24% probability to the bent excited state surface. The probability transfer is almost complete in 12 fs. The autocorrelation function for the absorption spectrum is significant for less than 5 fs and there is good agreement between the absorption spectrum calculated by the Fourier transform of the autocorrelation function and by the projection onto asymptotic states after 100 fs. Such an agreement suggests that the time-dependent Hartree approximation is a valid and good approximation for the problem. The absorption spectrum is resolved into I(2P3/2) and I*(2P1/2) components and these do not agree with the experimental results of Pitts and Baronavski, which supports previous conclusions that the Goldfield et al. ICN potentials are inadequate. Calculations of the CN rotational distribution as a function of the photolysis wavelength for both surfaces are also presented, and the results are interpreted using the wave packet picture. There is only qualitative agreement with the semiclassical results of Goldfield et al. and the recent time-independent, quantum coupled-channel calculations of Guo et al. © 1992 American Institute of Physics.
Wed, 01 Jan 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/953181992-01-01T00:00:00Z
- Useful results for the determination of excited state geometries from resonance Raman spectra: Application to inorganic complexeshttps://scholarbank.nus.edu.sg/handle/10635/95394Title: Useful results for the determination of excited state geometries from resonance Raman spectra: Application to inorganic complexes
Authors: Lee, S.-Y.; Lee, S.C.
Abstract: The time-dependent formulation of Raman scattering is used to derive simple expressions for fundamental and overtone intensities that depend on potential energy features in the Franck-Condon region and the homogeneous damping constant due to the bath modes. From the Raman excitation profiles, the dependence of the full width at half-maximum on the damping constant is calculated. The results are applied to the rich resonance Raman spectra and Raman excitation profiles of transition metal complexes, in particular, Cs3 [Re 2OCl10] and Cs4 [W2OCl 10], to determine the magnitude of the geometric changes occurring upon excitation of the molecule from the ground to the excited electronic state. For each compound, the multidimensional harmonic potential surface and damping constant derived for the excited electronic state are then used to simulate the observed Raman excitation profiles and resonance Raman spectrum. © 1992 American Institute of Physics.
Wed, 01 Jan 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/953941992-01-01T00:00:00Z
- Synthesis and conformational study of 1,1′-ethano-9-9′-bifluorenyl. Anti and gauche conformers of a 9,9′-bifluorenyl derivative and chair and twist conformers of a dibenzo-1,5-cyclooctadiene derivativehttps://scholarbank.nus.edu.sg/handle/10635/95047Title: Synthesis and conformational study of 1,1′-ethano-9-9′-bifluorenyl. Anti and gauche conformers of a 9,9′-bifluorenyl derivative and chair and twist conformers of a dibenzo-1,5-cyclooctadiene derivative
Authors: Lai, Y.-H.; Lee, S.-M.; Lee, S.-Y.; Yi, M.
Abstract: A Hofmann-type elimination of the sulphonium salt (18) under basic conditions led to the formation of a novel o-xylylene derivative (11) which dimerized regioselectively to give the bifluorenyl/dibenzo-1,5-cyclooctadiene derivative (3). The reaction is shown to be kinetically controlled and non-concerted. The two rigid conformers (3a) and (3b) were characterised by their 1H NMR spectra and they represent respectively the first observed examples of an anti bifluorenyl derivative and a twist dibenzo-1,5-cyclooctadiene derivative. A semiempirical molecular orbital PM3 calculation supported the observed results. Dynamic 1H NMR studies indicated an interconversion process (3a) ⇄ (3b) at higher temperatures involving a conformational barrier estimated at 65.2 kJ mol-1. © 1993.
Fri, 19 Mar 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/950471993-03-19T00:00:00Z
- Energy shift correction for the reflection approximationhttps://scholarbank.nus.edu.sg/handle/10635/76116Title: Energy shift correction for the reflection approximation
Authors: Lee, S.-Y.
Abstract: The neglect of the kinetic energy term in the usual reflection approximation leads to a shift of the reflection intensity towards lower energy compared to the exact intensity. A time-dependent formulation is used to derive the energy shift correction factors for absorption and Raman scattering. Examples are given to illustrate the new reflection formulas. © 1985 American Institute of Physics.
Tue, 01 Jan 1985 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/761161985-01-01T00:00:00Z
- Missing mode effect in resonance Raman excitation profilehttps://scholarbank.nus.edu.sg/handle/10635/94280Title: Missing mode effect in resonance Raman excitation profile
Authors: Lee, S.-Y.; Chang, H.-Y.
Abstract: Vibrational structure in the resonance Raman excitation profile (REP) of adenosinetriphosphate (ATP) in aqueous solution has been observed for both the 1333 and 1482 cm-1 modes, even though the absorption spectrum is structureless. The ∼2100 cm-1 spacing of the vibrational structure in both cases is much larger than the normal mode frequencies of the molecule. It is possible for such a vibrational structure to develop in a quasidiatomic (single mode) case, based on the reflection principle of the product wave functions |〈Q|I〉〈0|Q〉|2 appropriate for the fundamental REP, if the (dimensionless) displacement Δ between excited and ground state potentials is sufficiently large (Δ > 1) and the absorptive component of the REP dominates. However, this is not the case for ATP, where we show that the observed vibrational structure is due to an interplay of multiple modes. This "missing mode effect" (MIME) for REP, as m the case of luminescence spectra of large molecules, can be explained using the time-dependent correlation function picture of electronic transitions. The harmonic model is used and it is shown how the MIME frequency in the REP arises. The phenomenon is illustrated with ATP, where the harmonic parameters are derived from its resonance Raman spectrum at an excitation frequency of 260 nm, which are then used to calculate the absorption and REPs to compare with the experimental results. © 1994 American Institute of Physics.
Sat, 01 Jan 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/942801994-01-01T00:00:00Z
- Harmonic autocorrelation function: Application to diatomic photoelectron spectrahttps://scholarbank.nus.edu.sg/handle/10635/76275Title: Harmonic autocorrelation function: Application to diatomic photoelectron spectra
Authors: Lee, S.-Y.; Lim, S.-K.
Abstract: The time-dependent formulation of photoabsorption or photoionization is used to derive an analytical expression for the autocorrelation function of a Gaussian wave packet moving in an excited state harmonic potential. The short time limit of the harmonic autocorrelation function is used to analyze the experimental autocorrelation functions, obtained by the Fourier transformation of diatomic photoelectron spectra without the need for any corrections, to give information about the excited state surfaces of the ionic species. It yields both the frequency and the displacement in the equilibrium geometry of the local harmonic fit to the anharmonic excited state surface taken about the equilibrium geometry of the ground electronic state. The method can be viewed as the quantum mechanical analog to the classical analysis of the Franck-Condon picture of photoabsorption or photoionization of diatomic molecules in the harmonic approximation. It is (a) easy to use, (b) provides one bound for the displacement in the equilibrium geometry between excited and ground electronic states, (c) gives the displacement to within 10% of results obtained by rotational analysis, and (d) attaches a definite sign to the displacement which the conventional harmonic Franck-Condon analysis cannot do. The reflection autocorrelation function and the information that it carries about the excited state potential is also discussed. © 1988 American Institute of Physics.
Fri, 01 Jan 1988 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/762751988-01-01T00:00:00Z
- Dynamical theory of spectroscopy with femtosecond pulse excitation (I) - Dynamics of absorption and emission processeshttps://scholarbank.nus.edu.sg/handle/10635/76002Title: Dynamical theory of spectroscopy with femtosecond pulse excitation (I) - Dynamics of absorption and emission processes
Authors: Lu, J.; Lee, S.-Y.; Fan, K.
Abstract: A dynamical theory of spectroscopy with femtosecond pulse excitation is developed and is applied to studying the one-photon absorption and two-photon emission processes. Unlike the previous theories, this theory can treat all kinds of optical process from ultrashort pulse to CW limit in a consistent picture, because the exact equation of emission rate obtained from this theory can correctly reduce to the Kramers-Heisenberg-Dirac (KHD) expression.
Mon, 01 Sep 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/760021997-09-01T00:00:00Z