ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Mon, 27 May 2024 02:51:55 GMT2024-05-27T02:51:55Z50421- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- A test of the continuous configuration time-dependent self-consistent field (CC-TDSCF) method on the H + CH4 reactionhttps://scholarbank.nus.edu.sg/handle/10635/95696Title: A test of the continuous configuration time-dependent self-consistent field (CC-TDSCF) method on the H + CH4 reaction
Authors: Zhang, L.; Lee, S.-Y.; Zhang, D.H.
Abstract: The continuous configuration time-dependent self-consistent field (CC- TDSCF) method is employed to calculate the flux-flux autocorrelation functions for the H + CU4 reaction on the potential energy surface recently developed by Manthe and co-workers. We include up to 10 out of the total 12 degrees of freedom in our calculations, only with the doubly degenerate bending modes involving the motion of the hydrogens in nonreacting CH3 group excluded. Comparison of flux - flux autocorrelation functions obtained by using the exact dynamics method and the CC-TDSCF method shows that the CC- TDSCF method is capable of producing very accurate results. Our calculations clearly reveal that the CC-TDSCF method is a powerful approximation quantum dynamics method. It allows us to partition a big problem into several smaller ones. By changing partition systematically, one can investigate the correlations between different degrees of freedom. By grouping modes with strong correlations together as a cluster, one can systematically improve accuracy of the result. © 2006 American Chemical Society.
Thu, 27 Apr 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/956962006-04-27T00:00:00Z
- A full dimensional time-dependent wave packet study for the H4 four-center, collision induced dissociation, and single exchange reactions: Reaction probabilities for J=0https://scholarbank.nus.edu.sg/handle/10635/95622Title: A full dimensional time-dependent wave packet study for the H4 four-center, collision induced dissociation, and single exchange reactions: Reaction probabilities for J=0
Authors: Lu, Y.; Lee, S.-Y.; Zhang, D.H.
Abstract: A time-dependent initial state selected wave packet method has been developed to study the H2(v1=10-11,j1=0)+H 2 ′(v2=0,j2=0)→HH ′+HH′ four-center (4C) reaction, and two other competing reactions: the H2+H2 ′→ H+H+H2 ′ collision induced dissociation (CID) and the H2+H2 ′→H+HH ′+H′ single exchange (SE) reaction, in full six dimensions. Initial state-specific total reaction probabilities for these three competing reactions are presented for total angular momentum J=0 and the effects of reagent vibration on reactions are examined. It is found that (a) the CID process is the dominant process over the whole energy range considered in this study, but the 4C and SE processes also have non-negligible probabilities; (b) the SE process has a lower threshold energy than the 4C process, but the SE probability increases slower than the 4C probability as collision energy increases; (c) the vibrational excitation of H2(v1) is much more efficient than translational motion for promoting these processes, in particular to the CID process. © 2006 American Institute of Physics.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/956222006-01-01T00:00:00Z
- Semirigid vibrating rotor target calculation for reaction H+HOD→H2+OD, HD+OHhttps://scholarbank.nus.edu.sg/handle/10635/104856Title: Semirigid vibrating rotor target calculation for reaction H+HOD→H2+OD, HD+OH
Authors: Li, Y.-M.; Wang, M.-L.; Zhang, J.Z.H.; Zhang, D.H.
Abstract: The branching reaction on the Schatz-Elgersma potential energy surface was studied by the semigrid vibrating rotor target (SVRT). The reaction probabilities for producing two product branches were calculated and compared with the six dimensional dynamics. Comparison showed that SVRT reaction probabilitiesand cross-section for bith branching products were accurate within a wide range of collision energy.
Sun, 22 Apr 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1048562001-04-22T00:00:00Z
- Quantum wavepacket approach to chemical reaction dynamics. Perspective on "dynamics of the collinear H + H2 reaction. I. Probability density and flux"https://scholarbank.nus.edu.sg/handle/10635/104916Title: Quantum wavepacket approach to chemical reaction dynamics. Perspective on "dynamics of the collinear H + H2 reaction. I. Probability density and flux"
Authors: Zhang, J.Z.H.; Zhang, D.H.
Abstract: This paper presents an overview of the time-dependent quantum wavepacket approach to chemical reaction dynamics. After a brief review of some early works, the paper gives an up-to-date account of the recent development of computational methodologies in time-dependent quantum dynamics. The presentation of the paper focuses on the development of accurate or numerically exact time-dependent methods and their specific applications to tetraatomic reactions. After summarizing the current state-of-the-art time-dependent wavepacket approach, a perspective on future development is provided.
Tue, 01 Feb 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1049162000-02-01T00:00:00Z
- Theoretical study of the X+YCI (X, Y=H, D) reactionshttps://scholarbank.nus.edu.sg/handle/10635/104884Title: Theoretical study of the X+YCI (X, Y=H, D) reactions
Authors: Yao, L.; Han, K.-L.; Song, H.-S.; Zhang, D.-H.
Abstract: Time-dependent wave packet calculations for the reaction H+HC1 and its isotopic reactions are carried out on the potential energy surface (PES) of Bian and Werner (BW2) [Bain, W.; Werner, H.-J. J. Chem. Phys. 2000, 112, 220]. Reaction probabilities for the exchanged and abstraction channels are calculated from various initial rotational states of the reagent. Those have then been used to estimate reaction cross sections and rate constants which also are calculated and explained by the zero-point energy and the tunneling effect. The results of this work were compared with that of previous quasiclassical trajectory calculations and reaction dynamics experiments on the abstraction channel. In addition, the calculated rate constants are in reasonably good agreement with experimental measurements for both channels.
Wed, 01 Jan 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1048842003-01-01T00:00:00Z
- Theoretical study on the formation mechanism of resonance states for the Na + i2 → Na+ + i2 - systemhttps://scholarbank.nus.edu.sg/handle/10635/104885Title: Theoretical study on the formation mechanism of resonance states for the Na + i2 → Na+ + i2 - system
Authors: Cai, Z.; Wanyong, M.; Sun, X.; Feng, D.; Zhang, D.
Abstract: An extended LCAC-SW (linear combination of arrangement channels-scattering wavefunction) quantum scattering dynamic method combined with ab initio quantum chemical calculations has been used to study the formation mechanism of the resonance states for the ion-pair formation reaction Na + I2 → Na+ + I2 -. Resonance energy and resonance width or lifetime for the first resonance peak were calculated. Resonance can be identified to Feshbach resonance, and the physical interpretation has been given.
Wed, 01 Jan 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1048852003-01-01T00:00:00Z
- Dynasol: a visual quantum dynamics packagehttps://scholarbank.nus.edu.sg/handle/10635/104769Title: Dynasol: a visual quantum dynamics package
Authors: Peng, T.; Zhang, D.H.; Wang, D.-Y.; Li, Y.-M.; Zhang, J.Z.H.
Abstract: This paper gives an introduction to a new computer program - Dynasol (DynaSolver), a package of quantum dynamics program with graphical user interface (GUI). Dynasol is built on modern computational methods in quantum reaction dynamics and is integrated with graphical interface and visualization tools for X-window environment. The basic structure and instruction of using Dynasol are presented with simple examples. The available applications of Dynasol and the instructions on how to download and install the program are also provided.
Fri, 09 Jun 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1047692000-06-09T00:00:00Z
- The dynamics of the H+D2O→OD+HD reaction at 2.5 eV: Experiment and theoryhttps://scholarbank.nus.edu.sg/handle/10635/104875Title: The dynamics of the H+D2O→OD+HD reaction at 2.5 eV: Experiment and theory
Authors: Brouard, M.; Burak, I.; Minayev, D.; O'Keeffe, P.; Vallance, C.; Aoiz, F.J.; Bañares, L.; Castillo, J.F.; Zhang, D.H.; Collins, M.A.
Abstract: Fully quantum state-resolved OD angular scattering and kinetic energy release distributions for the hot H atom reaction with D2O at a mean collision energy of 2.48 eV are presented. In addition, OD quantum state population distributions and rotational alignment parameters as well as quantum state-averaged internal energy disposals are reported under the same conditions. The experimental data provide a stringent test for quasi-classical trajectory (QCT) scattering calculations, and of the potential energy surfaces they employ.
Wed, 15 Jan 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1048752003-01-15T00:00:00Z
- First-principles study of adsorption of methyl, coadsorption of methyl and hydrogen, and methane dissociation on Ni(1 0 0)https://scholarbank.nus.edu.sg/handle/10635/104787Title: First-principles study of adsorption of methyl, coadsorption of methyl and hydrogen, and methane dissociation on Ni(1 0 0)
Authors: Lai, W.; Xie, D.; Zhang, D.H.
Abstract: The adsorption of methyl on Ni(1 0 0) has been investigated using density functional theory calculations based on plane-wave expansion and pseudo-potential treatment. It was found that the bridge site with one of the hydrogen atoms near top site is most favorable. The calculated C-H symmetric stretching frequencies for the preferred bridge site showed a significant mode softening, thanks to the three-center bonding between C-H and Ni. The coadsorption of methyl and hydrogen on Ni(1 0 0) has also been calculated. The methyl at a bridge site with coadsorbed hydrogen at a hollow site was found to be preferred. In addition, the dissociation of methane on Ni(1 0 0) has been studied and the barrier height was found to be 0.73 eV, in good agreement with the recent experimental value of 0.61 eV. © 2005 Elsevier B.V. All rights reserved.
Thu, 01 Dec 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1047872005-12-01T00:00:00Z
- Quantum dynamics study of H2+CN → HCN+H reaction in full dimensionshttps://scholarbank.nus.edu.sg/handle/10635/104851Title: Quantum dynamics study of H2+CN → HCN+H reaction in full dimensions
Authors: Zhu, W.; Zhang, J.Z.H.; Zhang, Y.C.; Zhang, Y.B.; Zhan, L.X.; Zhang, S.L.; Zhang, D.H.
Abstract: Time-dependent (TD) quantum dynamics calculation for the title reaction has been carried out in full mathematical (six) dimensions on a new potential energy surface (denoted TSH3). Our numerical calculation shows that as far as total reaction probabilities and cross sections are concerned, the CN vibration behaves like a spectator bond when both reagents are at ground vibrational state. The vibrational excitation of CN slightly decreases the reaction probability and cross section while vibrational excitation of H2 considerably enhances the reaction probability and cross section. The reaction probability is enhanced by excitations of H2 rotation and more so of CN rotation. Overall, the reaction proceeds by a direct abstraction path without contribution from the insertion process. Comparison of our calculated rate constant with experimental measurements indicates that the effective barrier of the TSH3 PES for the title reaction is perhaps too high by about 0.3 kcal/mol. © 1998 American Institute of Physics.
Sun, 01 Mar 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1048511998-03-01T00:00:00Z
- Uniform J-shifting approach for calculating reaction rate constanthttps://scholarbank.nus.edu.sg/handle/10635/104896Title: Uniform J-shifting approach for calculating reaction rate constant
Authors: Zhang, D.H.; Zhang, J.Z.H.
Abstract: This paper presents a new uniform J-shifting approach for accurate calculation of rate constant in quantum dynamics study of chemical reaction. Instead of using a fixed shifting constant B in the standard J-shifting approach, the current method employs a temperature-dependent shifting constant which is obtained through an optimization procedure at a given temperature. By utilizing the calculated reaction probabilities at only a few total angular momentum values of J, the current approach automatically gives uniformly accurate rate constant across the entire range of temperature. Numerical studies of several benchmark reaction systems, including the H+H2, H2+OH and H2+CN reactions, show explicitly that the uniform J-shifting approach is far superior to the standard J-shifting approach and it provides a robust method for accurate and efficient calculation of reaction rate constant in rigorous quantum dynamics study of chemical reaction. © 1999 American Institute of Physics.
Thu, 22 Apr 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1048961999-04-22T00:00:00Z
- The quantum transition state wavepacket methodhttps://scholarbank.nus.edu.sg/handle/10635/104878Title: The quantum transition state wavepacket method
Authors: Light, J.C.; Zhang, D.H.
Abstract: The accurate calculation of thermal rate constants for reactions in the gas phase often requires both accurate potential energy surfaces (PESs) and the use of quantum mechanics, particularly in the case of light atom (H) transfers in reactions with activation energy barriers between reactants and products. The thermal rate constant k(T) can be calculated directly or as a thermal average over the cumulative reaction probability N(E). Both k(T) and N(E) can be calculated exactly and directly in terms of flux formulations first presented by Miller et al. In this paper we review the recent reformulation of the calculation of N(E) in terms of the time evolution of transition state wavepackets (TSWPs), which then provides a very effective method for reactions with activation energy barriers. This method requires a single time propagation for each TSWP contributing to the desired thermal rate constant from which the required contributions to N(E) for all E can be obtained. We then apply this to the calculation of N(E) and k(T) for the interesting four atom reaction H2(D2) + CN → HCN(DCN) + H(D). The system has a metastable well in the PES at the linear CNHH configuration. The results and a discussion of the influence of this secondary TS well are presented.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1048781998-01-01T00:00:00Z
- Interpolation of diabatic potential-energy surfaces: Quantum dynamics on ab initio surfaceshttps://scholarbank.nus.edu.sg/handle/10635/104800Title: Interpolation of diabatic potential-energy surfaces: Quantum dynamics on ab initio surfaces
Authors: Evenhuis, C.R.; Lin, X.; Zhang, D.H.; Yarkony, D.; Collins, M.A.
Abstract: A method for constructing diabatic potential-energy matrices from ab initio quantum chemistry data is described and tested for use in exact quantum reactive scattering. The method is a refinement of that presented in a previous paper, in that it accounts for the presence of the nonremovable derivative coupling. The accuracy of quantum dynamics on this type of diabatic potential is tested by comparison with an analytic model and for an ab initio description of the two lowest-energy states of H3. © 2005 American Institute of Physics.
Mon, 03 Oct 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1048002005-10-03T00:00:00Z
- Ab initio potential energy surface for the reactions between H2O and Hhttps://scholarbank.nus.edu.sg/handle/10635/104726Title: Ab initio potential energy surface for the reactions between H2O and H
Authors: Bettens, R.P.A.; Collins, M.A.; Jordan, M.J.T.; Zhang, D.H.
Abstract: An interpolated potential energy surfaces (PES2) for H2O which uses an additivity assumption to approximate the energy of this system at the QCISD(T)/6-311++G(3df,2pd) level of ab initio theory is presented. Comparison with experimental and other theoretical results shows that this surface is accurate at the few molecular configurations where comparison is possible. Classical and quantum dynamics calculations on the surfaces are presented.
Thu, 15 Jun 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1047262000-06-15T00:00:00Z
- Application of semirigid vibrating rotor target model to reaction of H+CH4→CH3+H2https://scholarbank.nus.edu.sg/handle/10635/104735Title: Application of semirigid vibrating rotor target model to reaction of H+CH4→CH3+H2
Authors: Wang, M.L.; Li, Y.; Zhang, J.Z.H.; Zhang, D.H.
Abstract: Time-dependent quantum scattering calculations using the semirigid vibrating rotor target (SVRT) model were carried out for the reaction H+CH4. Focus was on the reaction probability, cross-section, and rate constant from the initial ground state of the reagent. Results indicate that quantitatively reliable dynamic results can be obtained using the SVRT model in just a few mathematical dimensions.
Tue, 01 Aug 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1047352000-08-01T00:00:00Z
- Application of interpolated potential energy surfaces to quantum reactive scatteringhttps://scholarbank.nus.edu.sg/handle/10635/104734Title: Application of interpolated potential energy surfaces to quantum reactive scattering
Authors: Collins, M.A.; Zhang, D.H.
Abstract: The accuracy of an interpolation approach to molecular potential energy surfaces for quantum reactive scattering is demonstrated by comparison of the quantum reaction probability for a model surface and its interpolated approximation. Effective convergence of an ab initio surface with the size of the interpolation data set is demonstrated for the reaction BeH+H2 → BeH2+H. © 1999 American Institute of Physics.
Wed, 08 Dec 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1047341999-12-08T00:00:00Z
- Close-coupling time-dependent quantum dynamics study of the H + HCl reactionhttps://scholarbank.nus.edu.sg/handle/10635/104743Title: Close-coupling time-dependent quantum dynamics study of the H + HCl reaction
Authors: Yao, L.; Han, K.-L.; Song, H.-S.; Zhang, D.-H.
Abstract: The paper presents a theoretical study of the dynamics of the H + HCl system on the potential energy surface (PES) of Bian and Werner (Bian, W.; Werner, H. -J., J. Chem. Phys. 2000, 112, 220). A time-dependent wave packet approach was employed to calculate state-to-state reaction probabilities for the exchanged and abstraction channels. The most recent PES for the system has been used in the calculations. Reaction probabilities have also been calculated for several values of the total angular momentum J > 0. Those have then been used to estimate cross sections and rate constants for both channels. The calculated cross sections can be compared with the results of previous quasiclassical trajectory calculations and reaction dynamics experimental on the abstraction channel. In addition, the calculated rate constants are in the reasonably good agreement with experimental measurement.
Thu, 24 Apr 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1047432003-04-24T00:00:00Z
- Coherent classical-path description of deep tunnelinghttps://scholarbank.nus.edu.sg/handle/10635/104744Title: Coherent classical-path description of deep tunneling
Authors: Zhang, D.H.; Pollak, E.
Abstract: The deep quantum tunnelling was analyzed using coherent classical paths involving real time classical trajectories. It was observed that a (Gaussian) wave packet, localized on one side of a barrier with mean energy and an energy variance significantly smaller than the barrier height was scattered off the barrier. It was found that the classical path contribution became too small, when the barrier was not parabolic. The results show that the wave packet will always possess a tail whose energy is larger than the barrier light.
Fri, 01 Oct 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1047442004-10-01T00:00:00Z
- A new ab initio potential-energy surface of HO 2(X 2 A″) and quantum studies of HO 2 vibrational spectrum and rate constants for the H+O 22↔O+OH reactionshttps://scholarbank.nus.edu.sg/handle/10635/104718Title: A new ab initio potential-energy surface of HO 2(X 2 A″) and quantum studies of HO 2 vibrational spectrum and rate constants for the H+O 22↔O+OH reactions
Authors: Xu, C.; Xie, D.; Zhang, D.H.; Lin, S.Y.; Guo, H.
Abstract: A new global potential-energy surface for the ground electronic state of H O2 (X2 A″) has been developed by three-dimensional cubic spline interpolation of more than 15 000 ab initio points, which were calculated at the multireference configuration-interaction level with Davidson correction using the augmented correlation-consistent polarized valence quadruple zeta basis set. Low-lying vibrational states were obtained in this new potential using the Lanczos method and assigned. The calculated vibrational frequencies are in much better agreement with the available experimental band origins than those obtained from a previous potential. In addition, rate constants for the H+ O2 ↔O+OH reactions were obtained using a wave-packet-based statistical model. Reasonably good agreement with experimental data was obtained. These results demonstrate the accuracy of the potential. © 2005 American Institute of Physics.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1047182005-01-01T00:00:00Z
- Dependence of line shapes in femtosecond broadband stimulated Raman spectroscopy on pump-probe time delayhttps://scholarbank.nus.edu.sg/handle/10635/104754Title: Dependence of line shapes in femtosecond broadband stimulated Raman spectroscopy on pump-probe time delay
Authors: Yoon, S.; McCamant, D.W.; Kukura, P.; Mathies, R.A.; Zhang, D.; Lee, S.-Y.
Abstract: The effect of the time delay between the picosecond Raman pump and the femtosecond Stokes probe pulse on the Raman gain line shape in femtosecond broadband stimulated Raman spectroscopy (FSRS) is presented. Experimental data are obtained for cyclohexane to investigate the dependence of the FSRS line shape on this time delay. Theoretical simulations of the line shapes as a function of the time delay using the coupled wave theory agree well with experimental data, recovering broad line shapes at positive time delays and narrower bands with small Raman loss side wings at negative time delays. The analysis yields the lower bounds of the vibrational dephasing times of 2.0 ps and 0.65 ps for the 802 and 1027cm -1 modes for cyclohexane, respectively. The theoretical description and simulation using the coupled wave theory are also consistent with the observed Raman gain intensity profile over time delay, reaching the maximum at a slightly negative time delay (∼-1ps), and show that the coupled wave theory is a good model for describing FSRS. © 2005 American Institute of Physics.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1047542005-01-01T00:00:00Z
- Cross section for the H + H2O abstraction reaction: Experiment and theoryhttps://scholarbank.nus.edu.sg/handle/10635/104753Title: Cross section for the H + H2O abstraction reaction: Experiment and theory
Authors: Brouard, M.; Burak, I.; Marinakis, S.; Minayev, D.; O'Keeffe, P.; Vallance, C.; Aoiz, F.J.; Bañares, L.; Castillo, J.F.; Zhang, D.H.; Xie, D.; Yang, M.; Lee, S.-Y.; Collins, M.A.
Abstract: A state-of-the-art 5D quantum mechanical (QM) and quasiclassical trajectory (QCT) scattering calculations for the title reaction using the YZCL2 potential energy surface (PES) is presented. Calculated absolute cross sections and OH rotational distributions are compared with new experimental results obtained at a mean collision energy of 2.46 eV. Although the new theoretical and experimental data agree better than previous studies, there remains a factor of 2 discrepancy in the abstraction reaction cross section.
Fri, 07 Mar 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1047532003-03-07T00:00:00Z
- A first-principles potential energy surface and vibrational states for hydrogen on Cu(100)https://scholarbank.nus.edu.sg/handle/10635/104711Title: A first-principles potential energy surface and vibrational states for hydrogen on Cu(100)
Authors: Lai, W.; Xie, D.; Yang, J.; Zhang, D.H.
Abstract: The adiabatic potential energy surface (PES) for atomic hydrogen on Cu(100) surface was investigated using density function calculations. The vibrational band structure was calculated for the atomic hydrogen using a discrete variable representation. The calculated vibrational frequencies were found to be converging with the experimental results. The results show that the the vibrational states A1 0, A1 1, E 1 and B2 1 of H/Cu(100) exhibit strong localized character and very narrow bandwidths and the other excited vibrational states have considerable localized character and broad bandwidths.
Fri, 15 Oct 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1047112004-10-15T00:00:00Z
- Observation of Feshbach resonances in the F + H2 → HF + H Reactionhttps://scholarbank.nus.edu.sg/handle/10635/97400Title: Observation of Feshbach resonances in the F + H2 → HF + H Reaction
Authors: Qiu, M.; Ren, Z.; Che, L.; Dai, D.; Harich, S.A.; Wang, X.; Yang, X.; Xu, C.; Xie, D.; Gustafsson, M.; Skodje, R.T.; Sun, Z.; Zhang, D.H.
Abstract: Reaction resonances, or transiently stabilized transition-state structures, have proven highly challenging to capture experimentally. Here, we used the highly sensitive H atom Rydberg tagging time-of-flight method to conduct a crossed molecular beam scattering study of the F + H2 → HF + H reaction with full quantum-state resolution. Pronounced forward-scattered HF products in the v′ = 2 vibrational state were clearly observed at a collision energy of 0.52 kcal/mol; this was attributed to both the ground and the first excited Feshbach resonances trapped in the peculiar HF(v′ = B)-H′ vibrationally adiabatic potential, with substantial enhancement by constructive interference between the two resonances.
Fri, 10 Mar 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/974002006-03-10T00:00:00Z