ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Thu, 19 Sep 2019 17:34:13 GMT2019-09-19T17:34:13Z50351- High resolution FTIR spectrum of the ν5 and 2ν9 bands of HNO3https://scholarbank.nus.edu.sg/handle/10635/96793Title: High resolution FTIR spectrum of the ν5 and 2ν9 bands of HNO3
Authors: Tan, T.L.; Looi, E.C.; Lua, K.T.
Abstract: The Fourier transform infrared (FTIR) spectrum of the ν5 and 2ν9 bands of nitric acid (HNO3) has been measured with a resolution of 0.004 cm-1 in the frequency range of 856-910 cm-1. By fitting a total of 744 unperturbed transitions of ν5 with a standard deviation (SD) of 0.00051 cm-1, using a Watson Hamiltonian, a set of nine improved rovibrational constants for the upper state was obtained. Some transitions of 2ν9 were perturbed by a Femi resonance with the nearby ν5 state. A total of 280 unperturbed transitions of 2ν9 have been analyzed to provide nine rovibrational constants for the υ9 = 2 state with a SD of 0.00058 cm-1. The ν5 and 2ν9 bands are mainly A-type with band centres at 879.108200 ± 0.000045 and 896.44881 ± 0.00011 cm-1, respectively. A comparison of calculated line intensities of ν5 with measured values gives the transition moment as 0.155 ± 0.031 D and the integrated band intensity as 282 ± 56 cm-2 atm-1 (or 68 ± 14 km mol-1). The transition moment of the 2ν9 band is therefore estimated to be 0 17 ± 0.03 D which gives an integrated band intensity of 356 ± 71 cm-2 atm-1 (or 86 ± 17 km mol-1). © 1992.
Wed, 01 Jul 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967931992-07-01T00:00:00Z
- High resolution FTIR spectrum of the v6 band of deuterated formic acid (DCOOH)https://scholarbank.nus.edu.sg/handle/10635/96791Title: High resolution FTIR spectrum of the v6 band of deuterated formic acid (DCOOH)
Authors: Goh, K.L.; Ong, P.P.; Tan, T.L.; Teo, H.H.
Abstract: The high resolution FTIR spectrum of the v6 band of DCOOH has been measured with a resolution of 0.004 cm-1 in the spectral range of 920-1020 cm-1. The v6 band was found to be perturbed by the neighbouring v8 band situated at about 100 cm-1 lower. Using a Watson's A-reduced Hamiltonian in the F representation, and with the inclusion of a-, and b-Coriolis coupling constants, a simultaneous fit of v6 and v8 was performed, fitting a total of 1656 infrared transitions of v6 with an rms uncertainty of 0.00038 cm-1. A set of accurate rovibrational constants for v6 were obtained. The v6 band was analysed to be primarily A-typed with a band centre at 970.88931 ± 0.00003 cm-1. © 1999 Elsevier Science B.V. All rights reserved.
Fri, 01 Jan 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967911999-01-01T00:00:00Z
- High resolution FTIR spectrum of the v1 band of bromochloromethanehttps://scholarbank.nus.edu.sg/handle/10635/96790Title: High resolution FTIR spectrum of the v1 band of bromochloromethane
Authors: Wang, W.F.; Tan, T.L.; Tan, B.L.; Ong, P.P.
Abstract: The IR spectrum of the v1 band of natural bromochloromethane (CH2BrCl) has been recorded at a resolution of 0.008 cm-1 in the region 2940-3060 cm-1 on a BOMEM DA3.002 Fourier-transform spectrometer. The rovibrational analysis on the strong Q branch of this B-type band has been performed in the prolate symmetry top approximation due to the fairly small difference between constants B and C. A normal linear least-square fitting of the identified P,RQK(J) clusters provided the corresponding excited state molecular parameters for three of the four naturally existing isotopomers of bromochloromethane with a standard error of about 0.02cm-1.
Fri, 01 Mar 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967901996-03-01T00:00:00Z
- High resolution FTIR spectrum of the ν6 band of HNO3https://scholarbank.nus.edu.sg/handle/10635/96794Title: High resolution FTIR spectrum of the ν6 band of HNO3
Authors: Tan, T.L.; Wang, W.F.; Looi, B.C.; Ong, P.P.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967941996-01-01T00:00:00Z
- Hot-band spectrum of N2O near 589 cm-1https://scholarbank.nus.edu.sg/handle/10635/96831Title: Hot-band spectrum of N2O near 589 cm-1
Authors: Tan, T.L.; Looi, E.C.; Lua, K.T.
Wed, 01 Jul 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/968311992-07-01T00:00:00Z
- FTIR Spectrum of the v4 Band of DCOODhttps://scholarbank.nus.edu.sg/handle/10635/96682Title: FTIR Spectrum of the v4 Band of DCOOD
Authors: Tan, T.L.; Goh, K.L.; Ong, P.P.; Teo, H.H.
Abstract: The FTIR spectrum of the v4 band of deuterated formic acid (DCOOD) has been measured with a resolution of 0.004 cm-1 in the frequency range of 1120 to 1220 cm-1. A total of 1866 assigned transitions have been analyzed and fitted using a Watson's A-reduced Hamiltonian in the Ir representation to derive rovibrational constants for the upper state (v4 = 1) with a standard deviation of 0.00036 cm-1. In the course of the analysis, the constants for the ground state were improved by a simultaneous fit of microwave frequencies and combination differences from the infrared measurements. Due to the relatively unperturbed nature of the band, the constants can be used to accurately calculate the infrared line positions for the whole band. Although the band is a hybrid type A and B, only a-type transitions were strong enough to be observed. The band center is at 1170.79980 ± 0.00002 cm-1. © 1999 Academic Press.
Tue, 01 Jun 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/966821999-06-01T00:00:00Z
- Improved spectroscopic constants for the ν2 infrared band of HNO3https://scholarbank.nus.edu.sg/handle/10635/96885Title: Improved spectroscopic constants for the ν2 infrared band of HNO3
Authors: Tan, T.L.; Looi, E.C.; Lua, K.T.
Thu, 01 Oct 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/968851992-10-01T00:00:00Z
- High-Resolution FTIR Spectrum of the ν5 Band of HCOODhttps://scholarbank.nus.edu.sg/handle/10635/96821Title: High-Resolution FTIR Spectrum of the ν5 Band of HCOOD
Authors: Goh, K.L.; Ong, P.P.; Tan, T.L.; Teo, H.H.; Wang, W.F.
Abstract: The high-resolution Fourier transform infrared spectrum of HCOOD has been measured in the ν5 region between 1120 and 1220 cm-1 with a resolution of 0.004 cm-1. As expected for an in-plane vibrational fundamental mode, the ν5 band is a hybrid band consisting of both a-type and b-type transitions. Using the Watson's A-reduced Hamiltonian in the Ir representation, 1943 infrared transitions have been assigned and fitted to give 12 rovibrational constants for the ν5 = 1 state. The ν5 band is primarily A type with a band center at 1177.09378 ± 0.00002 cm-1. It is found that ν5 is slightly perturbed by the nearby 2ν7. About 90 perturbed transitions were identified. © 1998 Academic Press.
Thu, 01 Oct 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/968211998-10-01T00:00:00Z
- Experimental transverse diffusion and Monte Carlo simulation studies of Rb+ swarm drifting in He gashttps://scholarbank.nus.edu.sg/handle/10635/96571Title: Experimental transverse diffusion and Monte Carlo simulation studies of Rb+ swarm drifting in He gas
Authors: Ong, P.P.; Tan, T.L.
Abstract: Experimental measurements have been made of the transverse diffusion of Rb+ swarms drifting in He gas at E/N (drift field to gas concentration ratio) values ranging from 5 to 500 Td, and at gas temperatures between 302 and 304 K. Results with typical errors of ±3% are reported. In addition, Monte Carlo simulation (MCS) calculations were made of the mobility, transverse, and longitudinal diffusion coefficients of Rb+ in He using two recently proposed interaction potentials. Comparisons of the MCS results with available experimental data give an indication of the validity and accuracy of the respective assumed interaction potentials at different interatomic distances. Further calculations of the transverse and longitudinal diffusion coefficients from known mobility values using the generalized Einstein relations based on the three-temperature theory suggest that the theory is fairly accurate at all E/N values despite the high ion-neutral mass ratio. © 1995 American Institute of Physics.
Sun, 01 Jan 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/965711995-01-01T00:00:00Z
- Infrared Analysis of the Anharmonic Resonance between ν8 + ν9 and the Dark State ν6 + ν7 of HNO3https://scholarbank.nus.edu.sg/handle/10635/96934Title: Infrared Analysis of the Anharmonic Resonance between ν8 + ν9 and the Dark State ν6 + ν7 of HNO3
Authors: Wang, W.F.; Ong, P.P.; Tan, T.L.; Looi, E.C.; Teo, H.H.
Abstract: The high-resolution FTIR spectrum of the ν8 + ν9 band of HNO3 around 1205 cm-1 has been measured and analyzed. The bright state was found to be strongly perturbed by its neighboring dark state ν6 + ν7 at the coincident levels. Taking account of the ΔK = ±2 anharmonic resonance, a simultaneous fit of ν8 + ν9 and ν6 + ν7 was performed leading to a good reproduction of the ν8 + ν9 band with a rms uncertainty of 0.00046 cm-1. A set of rovibrational constants for ν8 + ν9 were accurately determined, while for ν6 + ν7 the rotational constant B and the band origin were obtained. © 1997 Academic Press.
Sun, 01 Jun 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/969341997-06-01T00:00:00Z
- Studies of rubidium aluminosilicates as thermionic emitters of Rb+ ionshttps://scholarbank.nus.edu.sg/handle/10635/98072Title: Studies of rubidium aluminosilicates as thermionic emitters of Rb+ ions
Authors: Tan, T.L.; Ong, P.P.; Fong, T.M.; Soo, K.A.
Abstract: Filament sources of Rb+ ions were created using 90% Pt-10% Rh gauze coated with synthetic rubidium aluminosilicate compounds of various compositions. The performance characteristics of these compounds as thermionic emission sources of Rb+ ions based on total emission current and purity of ion emission as functions of time were studied and compared. In addition, these characteristics were investigated of β-eucryptite (Rb2O·Al2O3·2SiO2) and spodumene (Rb2O·Al2O3·4SiO2) samples at four different filament surface temperatures. It was concluded that the β-eucryptite composition of rubidium aluminosilicate gives the most satisfactory results as a Rb+ ion emitter at a temperature of 1100°C. © 1994.
Thu, 30 Jun 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/980721994-06-30T00:00:00Z
- The High-Resolution Infrared Spectrum of the v5 Band of Deuterated Formic Acid (DCOOH)https://scholarbank.nus.edu.sg/handle/10635/98279Title: The High-Resolution Infrared Spectrum of the v5 Band of Deuterated Formic Acid (DCOOH)
Authors: Goh, K.L.; Ong, P.P.; Tan, T.L.; Wang, W.F.; Teo, H.H.
Abstract: The Fourier transform infrared spectrum of the v5 band of deuterated formic acid (DCOOH) has been measured with a resolution of 0.004 cm-1 in the frequency range of 1090-1180 cm-1. Using a Watson's A-reduced Hamiltonian in the Ir representation, a total of 1731 assigned unperturbed transitions have been analyzed to provide rovibrational constants for the upper state (v5 = 1) with a standard deviation of 0.000363 cm-1. The band is A type with an unperturbed band center at 1142.31075 ± 0.00002 cm-1. The band is expected to be perturbed by a nearby v4 band through a Fermi resonance term and possibly a Coriolis term. The resonance is particularly noticeable for Ka = 10, and 11, at high J values. About 215 perturbed lines were identified but they were not included in the final fit. © 1998 Academic Press.
Wed, 01 Jul 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/982791998-07-01T00:00:00Z
- Thermionic oxide sources of Al+, Ga+, In+, and Tl+https://scholarbank.nus.edu.sg/handle/10635/98381Title: Thermionic oxide sources of Al+, Ga+, In+, and Tl+
Authors: Tan, T.L.; Zhou, Z.L.; Ong, P.P.
Abstract: Oxides (Al2O3, Ga2O3, In2O3, and Tl2O3) of Group IIIA metals were coated on tungsten filaments to form thermionic emitters of purely ground state Al+, Ga+, In+ and Tl+ ions respectively. Variations of total ion emission current and ion purity with source filament temperature, and with time were studied. A very pure (99.9%) source of Al+(1 S0) could be obtained from the Al2O3-coated filament when heated to 2200°C but the filament was short lived. A stable ion current and a purity between 92% and 96% of Al+ could be produced at a lower temperature of 2000°C after 100 min of heating. At 1900°C, the Ga2O3-coated filament could produce Ga+(1S0) ions of 98% purity but its ion current was unstable with time. However, in the lower range of 1600-1820°C, a more stable Ga+ ion current of about 80% purity could be obtained shortly after heating. For the In2O3-coated filament, the purity of In+(1S0) ions reached a maximum of 90% at 1580°C while the total ion current increased to a maximum of 2900 nA at 1690°C. A very stable In+ ion current could be obtained at 1580°C. The Tl2O3-coated filament using tungsten or tantalum wires was found to be unsuitable as a source of Tl+ ions. © 1995.
Fri, 31 Mar 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983811995-03-31T00:00:00Z
- The ν1 Band of HOBrhttps://scholarbank.nus.edu.sg/handle/10635/98330Title: The ν1 Band of HOBr
Authors: Cohen, E.A.; Mcrae, G.A.; Tan, T.L.; Friedl, R.R.; Johns, J.W.C.; Noel, M.
Abstract: The ν1 band of HOBr centered at 3614.903 cm-1 has been observed at 0.006 cm-1 resolution. The band is a hybrid type with |(∂μb/∂Q1)/(∂μa/ ∂Q1)| ≈ 0.84. The spectra of both bromine isotopes have been simultaneously fitted with a single calculation which includes all the previously reported rotational transitions. There appear to be no strong local perturbations to complicate the fitting of the line positions. Precise parameters are reported for the upper states as well as improved parameters for the ground states of both species. There is a prominent Herman-Wallis effect for the b-type transitions, which is well described by linear and quadratic terms in Ka. The equilibrium structure has been calculated. © 1995 Academic Press. All rights reserved.
Fri, 01 Sep 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983301995-09-01T00:00:00Z
- The ν2 bands of HD18O and D2 18O: Rovibrational constants and additional transitionshttps://scholarbank.nus.edu.sg/handle/10635/98331Title: The ν2 bands of HD18O and D2 18O: Rovibrational constants and additional transitions
Authors: Wang, W.F.; Tan, T.L.; Tan, B.L.; Ong, P.P.
Fri, 01 Mar 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983311996-03-01T00:00:00Z
- The v2 and v8 + v10 bands of CF2=CH2https://scholarbank.nus.edu.sg/handle/10635/98328Title: The v2 and v8 + v10 bands of CF2=CH2
Authors: Wang, W.F.; Tan, T.L.; Ong, P.P.
Abstract: The high-resolution FTIR spectrum of CF2=CH2 was measured and analyzed in the Fermi interacting v2 and v8 + v10 bands around 1735 cm-1. Both bands have strong infrared absorption with an A-type appearance. Watson's A-reduced Hamiltonian in the Ir representation was employed in the computation of the energy levels, taking into account the Fermi resonance contribution. A total of 2119 v2 transitions and 2056 v8 + v10 transitions were eventually assigned with a rms deviation of 0.00075 cm-1. In a nonlinear least-squares fit, accurate rovibrational constants of the upper states were determined with the band origins v2 = 1728.49829 ± 0.00005 cm-1 and v8 + v10 = 1741.50207 ± 0.00004 cm-1. Finally, a set of equilibrium rotational constants of CF2=CH2 were derived. © 1997 Academic Press, Inc.
Wed, 01 Jan 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983281997-01-01T00:00:00Z
- Transport properties of Rb+ ions in Ne and Ar gaseshttps://scholarbank.nus.edu.sg/handle/10635/98451Title: Transport properties of Rb+ ions in Ne and Ar gases
Authors: Tan, T.L.; Ong, P.P.; Zhou, Z.L.
Abstract: The ratio of the transverse diffusion coefficient to mobility, DT/K, has been experimentally measured for Rb+ ions drifting in Ne and Ar gases in the presence of a uniform electric field. Results at 303 K are reported at electric field to neutral gas density ratio, E/N, values ranging from 5 to 500 Td for both Rb+Ne and Rb+Ar systems. The reduced mobility KO and the ratios of the longitudinal and transverse diffusion coefficients to mobility, DL/K and DT/K respectively, were calculated for both Rb+Ne and Rb+Ar systems with a Monte Carlo simulation (MCS) technique which used the interaction potential of Koutselos, Mason and Viehland (KMV) (J. Chem. Phys., 93 (1990) 7125) as input. The accuracy of this potential has been evaluated by comparing the DT/K results to the experimentally determined values. The KMV potential appears to be a good representation of the actual potential in the whole E/N range (5-500 Td) for Rb+Ne but only in the 5-350 Td range for Rb+Ar. Values of DL/K and DT/K were also derived using KO obtained from the present MCS calculations and from experimental data available in the literature, employing the generalised Einstein relations (GER) based on the three-temperature theory. In the E/N range studied for both Rb+Ne and Rb+Ar systems, the accuracy of the experimental measurements of DT/K is estimated to be ±3% and that of the MCS calculations to be ±2.5%. © 1995.
Fri, 15 Dec 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984511995-12-15T00:00:00Z
- Transport properties and interaction potential for Na+ ions in Xe gashttps://scholarbank.nus.edu.sg/handle/10635/98446Title: Transport properties and interaction potential for Na+ ions in Xe gas
Authors: Tan, T.L.; Ong, P.P.; Hogan, M.J.
Abstract: The ratio, DT/K, of the transverse diffusion coefficient to mobility for Na+ ions drifting in Xe gas has been experimentally measured. Inevitable longitudinal end effects present in the drift tube were duly corrected for. Results at ∼303 K are reported at electric field to neutral gas density ratios, E/N, ranging from 5 to 440 Td. Furthermore, elaborate calculations of the reduced mobility, K0, the ratio, D L/K, of the longitudinal diffusion coefficient to mobility, and DT/K were calculated with a Monte Carlo simulation (MCS) method which used the interaction potential of Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)] as input. The accuracy of this potential has been evaluated by comparing the results with the experimental data and those calculated using the generalized Einstein relations technique. Agreement within 3% between the experimental values of DT/K and those from MCS calculations for the whole range of E/N suggests that the interaction potential represents fairly well the true potential. The error of the experimental measurements of DT/K is estimated to be better than 3.5% and that of the MCS calculations is better than 1% for K0 and 2.5% for D T,L/K. © 1994 American Institute of Physics.
Sat, 01 Jan 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984461994-01-01T00:00:00Z
- Transverse diffusion measurements and Monte Carlo simulation studies of Rb+ ions in Kr and Xehttps://scholarbank.nus.edu.sg/handle/10635/98454Title: Transverse diffusion measurements and Monte Carlo simulation studies of Rb+ ions in Kr and Xe
Authors: Tan, T.L.; Ong, P.P.
Abstract: The ratio of the transverse diffusion coefficient to the mobility (D T/K) for Rb+ ions drifting in Kr and Xe gases at about 303 K has been measured at electric field to neutral gas density ratio (E/N) values ranging from 5 to 500 Td. Calculations of the reduced mobility (K0) and the ratios of the longitudinal and transverse diffusion coefficients to mobility (DL/K and DT/K, respectively) for both Rb +-Kr and Rb+-Xe systems were made using a Monte Carlo simulation (MCS) technique and the interaction potential of Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)]. Furthermore, DL/K and DT/K values were derived from K0 values obtained from the present MCS calculations and from experimental results reported in the literature, using the generalized Einstein relations which are based on the three-temperature theory. For the Rb+-Kr system, the experimental values of DT/K were found to be 2%-4% higher than those from MCS calculations for EIN values above 120 Td. For the Rb+-Xe system, the experimental DT/K values were similarly higher than the MCS values in the range 90-220 Td. Given that the standard error of the experimental measurements of DT/K is estimated to be better than 3% and that of the MCS calculations is better than 2.5%, the agreement between the present experimental DT/K data and those from MCS calculations can be considered to be fairly good. The interaction potential of Koutselos, Mason, and Viehland therefore appears to represent well the actual potential for both Rb+-Kr and Rb+-Xe systems. © 1995 American Institute of Physics.
Sun, 01 Jan 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984541995-01-01T00:00:00Z
- Longitudinal and transverse diffusion coefficients for Li+ ion swarms in Kr gashttps://scholarbank.nus.edu.sg/handle/10635/97094Title: Longitudinal and transverse diffusion coefficients for Li+ ion swarms in Kr gas
Authors: Tan, T.L.; Ong, P.P.; Li, M.M.
Abstract: The ratio of the transverse diffusion coefficient to mobility, DT/K at 309 K for Li+ ion swarms drifting in Kr gas in the E/N (electric field to neutral gas number density ratio) range of 5 to 170 Td, was experimentally determined with an overall accuracy of ±4%. The DT/K results were effectively corrected for longitudinal end effects present appreciably in the drift tube by an analysis which requires the measurement of variance x2 of the transverse ion-current density profile at different drift lengths z and the derivation of the magnitude a2 of the end effects. Good agreement of the results with those calculated by Monte Carlo simulations (MCS) using an established interaction potential demonstrates the accuracy and reliability of the present DT/K results. In addition, elaborate calculations of the reduced mobility K0 and ratio DL/K of the longitudinal diffusion coefficient to mobility of the Li+-Kr system are calculated with the MCS method. The accuracy of the MCS calculations is estimated to be ±2.5%. The calculated DL/K values are compared with the experimental data available in the literature. Both DT/K and DL/K values for Li+ in Kr were also derived using reduced mobility K0 data obtained from the MCS calculations and from experimental data, employing the generalized Einstein relations based on the three-temperature theory. © 1995 The American Physical Society.
Sun, 01 Jan 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/970941995-01-01T00:00:00Z
- Hot-Band Spectrum of CO2 near 700 cm-1 and the ν1 Band of OC34Shttps://scholarbank.nus.edu.sg/handle/10635/96830Title: Hot-Band Spectrum of CO2 near 700 cm-1 and the ν1 Band of OC34S
Authors: Tan, T.L.; Looi, E.C.; Lee, K.K.
Fri, 01 Jan 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/968301993-01-01T00:00:00Z
- Thermionic aluminosilicate sources of Tl+ ionshttps://scholarbank.nus.edu.sg/handle/10635/98380Title: Thermionic aluminosilicate sources of Tl+ ions
Authors: Zhou, Z.L.; Tan, T.L.; Ong, P.P.
Abstract: Thermionic filament sources of Tl+ ions were made using tungsten wire coated with synthetic thallium aluminosilicates in the β-eucryptite (Tl2OAl2O32SiO2) and two other compositions (2Tl2OAl2O32SiO2 and 2Tl2OAl2O34SiO2). Three different methods for the production of aluminosilicate melts were used. The performance characteristics as thermionic emission sources of Tl+ ions based on total emission current and purity of ion emission as functions of time and filament surface temperature were studied and compared. Our results indicated that the sample of composition ratio of 2Tl2OAl2O 32SiO2, which was produced by resistance heating under atmospheric pressure in air, is an optimum Tl+ ion source at temperatures between 1150 and 1350°C after 150 h of continuous heating. © 1995 American Institute of Physics.
Sun, 01 Jan 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983801995-01-01T00:00:00Z
- Transverse diffusion of Li + ion swarms in Xe gashttps://scholarbank.nus.edu.sg/handle/10635/98455Title: Transverse diffusion of Li + ion swarms in Xe gas
Authors: Tan, T.L.; Ong, P.P.
Abstract: In our transverse diffusion measurements of Li+ ions in Xe gas, appreciable longitudinal end effects were found throughout the whole range of E/N (electric field to neutral gas number density ratio) studied, i.e. 5-150 Td. By applying a known linear relationship of the measured variance (x 2) of the transverse ion current density profile with drift length z, the magnitude a 2 of the end effects can be numerically derived. The ratio of the transverse diffusion coefficient to mobility, D T/K, at 309 K for the Li+-Xe system were eventually corrected for end effects by an analysis which requires measured (x 2) values and a 2. The value of a 2 is assumed to vary linearly with E/N. The corrected D T/K values are determined with an overall accuracy of +or-4%. The self-consistency and the good agreement of the results with those calculated by Monte Carlo simulations (MCS) bears evidence of the accuracy and reliability of the D T/K results. The accuracy of the MCS calculations is estimated to be +or-2.5%. The D T/K values for Li + in Xe were also derived using reduced mobility K 0 data obtained from the MCS calculations and from experimental data available in the literature, employing the generalized Einstein relations (GER) based on the three-temperature theory. © 1995 IOP Publishing Ltd.
Mon, 14 Aug 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984551995-08-14T00:00:00Z
- Reexamination of the Li+-He interaction potentialhttps://scholarbank.nus.edu.sg/handle/10635/97787Title: Reexamination of the Li+-He interaction potential
Authors: Ong, P.P.; Hogan, M.J.; Tan, T.L.
Abstract: Using various recently proposed interaction potentials for the Li+-He system, elaborate calculations of the mobility, longitudinal, and transverse diffusion coefficients of Li+ swarms in helium have been made by high-speed Monte Carlo simulations (MCS's). In addition, the transverse diffusion coefficients for this ion-neutral-atom pair have been experimentally measured with total errors of ±3%. The close agreement of the present experimental results with those of Skullerud, Eide, and Stefansson [J. Phys. D 19, 197 (1986)] as well as the faithful MCS reproduction of all three transport coefficients using the interaction potential proposed by Larsen et al. [J. Phys. B 21, 2519 (1988)] over the entire range of E/N (electric field to neutral-particle number density ratio) studied not only provides confirmation of their transport coefficient values, but also lends strong support for their proposed interaction potential. In comparison, the more recent potentials of Ahlrichs et al. [J. Chem. Phys. 88, 6290 (1988)] and of Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)] did not reproduce the experimental data quite as well. As a benchmark the MCS calculations have also provided evidence of the accuracy of the Kramers-Moyal expansion method in calculating the transport coefficients. © 1992 The American Physical Society.
Wed, 01 Jan 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977871992-01-01T00:00:00Z
- Oxides as thermionic sources of Mg+, Ca+, Sr +, and Ba+ ionshttps://scholarbank.nus.edu.sg/handle/10635/97481Title: Oxides as thermionic sources of Mg+, Ca+, Sr +, and Ba+ ions
Authors: Tan, T.L.; Zhou, Z.L.; Ong, P.P.
Abstract: Group II metal oxides (MgO, CaO, SrO, and BaO) were coated on tungsten or tantalum filaments to form thermionic emitters of positive metal ions. The choice between tungsten and tantalum for optimum performance was empirically found to depend on the oxide material. Total ion emission current and ion purity were generally found to increase with temperature. A stable source of high purity (up to 97%) Ba+ ions could be obtained from the BaO-coated filament at 1800 °C after 150 min of heating. At 1600 °C, the SrO-coated filament could produce a relatively stable ion current and purity of 97% of Sr+ ions. Very pure (99.8%) Ca+ ions were emitted at 1950 °C. However more stable ion current though less pure ions (87% of Ca + at 1800 °C) were obtained at lower temperatures. MgO-coated filaments using tungsten or tantalum wires were found to be unsuitable as a source of Mg+ ions. All the filaments of MgO, CaO, SrO, and BaO were found to produce larger ion current and higher ion purity at higher temperatures. In general, the relative isotopic abundances of ions produced by a thermionic source are reproduced by the natural isotopic abundances of the corresponding metal. It implies that the slight differences in the nuclear masses of the isotopes do not introduce any significant effect on their ion production efficiency. Between tantalum and tungsten as a choice for the filament material, tantalum was found to be a better choice for Ba+ and Sr+ ions, while tungsten was better for Ca+. © 1995 American Institute of Physics.
Sun, 01 Jan 1995 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/974811995-01-01T00:00:00Z
- Transport properties of Na+ ions in Kr gashttps://scholarbank.nus.edu.sg/handle/10635/98450Title: Transport properties of Na+ ions in Kr gas
Authors: Tan, T.L.; Ong, P.P.; Hogan, M.J.
Abstract: The transverse-diffusion coefficients for Na+ ions drifting in Kr gas have been experimentally measured with estimated accuracies of better than 3% at E/N values ranging from 5 to 500 Td (1 Td=10-21 V m2) at about 303 K. In addition, elaborate calculations of the transport properties for the Na+-Kr system have been made by using Monte Carlo simulations (MCSs) and the generalized Einstein-relation techniques. The experimental results are compared with values obtained from MCSs using the interaction potential of Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)] as input. Agreement within 3% for the entire range of E/N is observed in the comparisons. MCS-calculated values of longitudinal-diffusion coefficients are also compared with those determined experimentally by Thackston et al. [J. Chem. Phys. 73, 2012 (1980)]. © 1993 The American Physical Society.
Fri, 01 Jan 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984501993-01-01T00:00:00Z
- v3 band of DCOOHhttps://scholarbank.nus.edu.sg/handle/10635/98541Title: v3 band of DCOOH
Authors: Goh, K.L.; Ong, P.P.; Tan, T.L.
Abstract: The high resolution Fourier transform infrared (FTIR) spectrum of the v3 band of DCOOH has been measured with a resolution of 0.004 cm-1 in the spectral range 1670-1810 cm-1. Using the Watson's A-reduced Hamiltonian in the Ir representation, 713 infrared transitions have been assigned and fitted to provide rovibrational constants for the v3 = 1 state with a standard deviation of 0.000439 cm-1. The v3 band centre was found at 1725.87497±0.00003 cm-1. The band is perturbed by the 2v8 band, situated at 1762.9 cm-1, through Fermi resonance and possibly a Coriolis term. Perturbations of v3 by v5+v7 and v5+v9 are also expected. About 280 perturbed v3 lines were identified and excluded in the final fit.
Mon, 01 Nov 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985411999-11-01T00:00:00Z
- Interatomic potential and transport properties of Na + ions in He/elhttps://scholarbank.nus.edu.sg/handle/10635/92728Title: Interatomic potential and transport properties of Na + ions in He/el
Authors: Ong, P.P.; Tan, T.L.; Lam, K.Y.
Abstract: Hitherto unavailable experimental values of the ratio, DT/K, of the transverse diffusion coefficient to mobility for Na + ions drifting in helium gas are reported. Results were obtained with estimated accuracies of better than 3% at temperatures between 302 and 304 K, and at electric field to neutral gas density ratios, E/N, ranging from 5 to 400 Td. By an independent approach, the three transport parameters are also computed by Monte Carlo simulation using the modified Tang-Toennies potential and the Koutselos, Mason and Viehland potential as input, separately. Comparison between the simulated results and available experimental data suggests that the latter potential represents fairly well the true interaction in the long and intermediate ranges, but its short-range repulsive region is too soft. © 1993 IOP Publishing Ltd.
Sat, 28 Aug 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/927281993-08-28T00:00:00Z
- Diffusion coefficients and interaction potential for Na + ions in argon gashttps://scholarbank.nus.edu.sg/handle/10635/96224Title: Diffusion coefficients and interaction potential for Na + ions in argon gas
Authors: Tan, T.L.; Ong, P.P.
Abstract: Experimental values of the ratio, D T/K, of the transverse diffusion coefficient to mobility for Na + ions drifting in Ar gas have been determined with greater accuracy and at higher E/N (electric field to neutral gas density ratio) regions than previously. Results at a drift tube temperature of about 303 K are reported with estimated accuracies of +or-3% at E/N values ranging from 5 to 500 Td. Furthermore, the reduced mobility, K 0, And the ratios D T,L/K of the transverse and longitudinal diffusion coefficients respectively to mobility, were calculated using Monte Carlo simulations (MCS). Comparisons between the experimental values of D T/K and those calculated using the interaction potential of Koutselos, Mason and Viehland (1990) suggest that this interaction is a good representation of the true potential in the long and intermediate ranges. © 1994 IOP Publishing Ltd.
Thu, 28 Apr 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/962241994-04-28T00:00:00Z
- Experimental and Monte Carlo simulation studies of transport properties of Cs+ swarms drifting in Ne and Ar gaseshttps://scholarbank.nus.edu.sg/handle/10635/96550Title: Experimental and Monte Carlo simulation studies of transport properties of Cs+ swarms drifting in Ne and Ar gases
Authors: Zhou, Z.L.; Ong, P.P.; Li, M.M.; Tan, T.L.
Abstract: The ratio of the transverse diffusion coefficient to the mobility, DT/K, has been experimentally determined for Cs+ ions drifting in Ne and Ar gases, in the presence of a uniform electric field. Results at 303 K are reported for electric field-to-neutral gas number density ratio E/N range 5-600 Td, with an overall accuracy of ±3%. The DT/K results were effectively corrected for longitudinal end effects present in the drift tube. In addition, Monte Carlo simulation (MCS) calculations were performed for the mobility and for transverse and longitudinal diffusion coefficients using respectively the Koutselos, Mason and Viehland (KMV) interaction potential and a modified Tang-Toennies (MTT) interaction potential as input. The accuracy of the MCS calculations is estimated to be within 1% for K, 2% for DT/K and 3% for DL/K. Comparisons of the MCS results with available experimental data give an indication of the validity and accuracy of the respective assumed interaction potential at different interatomic distances. The calculated results did not reproduce the experimental data very well, suggesting that both potentials should be modified.
Sun, 14 Jul 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/965501996-07-14T00:00:00Z
- Aluminosilicate sources of Cs+ ionshttps://scholarbank.nus.edu.sg/handle/10635/95748Title: Aluminosilicate sources of Cs+ ions
Authors: Ong, P.P.; Tan, T.L.
Abstract: Synthetic cesium aluminosilicates in the form of β-eucryptite (Cs 2O·Al2O3·2SiO2) and spodumene (Cs2O·Al2O3·4SiO 2) were used to construct thermionic emitters of Cs+ ions. Total ion emission current and purity of ion emission of Cs+ ions for these two forms of aluminosilicates were studied and compared at four different material surface temperatures over 50 h of continuous heating. In addition, the ion emission characteristics were investigated for three other compositions of cesium aluminosilicates. It was revealed that as a Cs + ion source, β-eucryptite gives the optimum ion emission at the temperature of 1100°C. © 1994 American Institute of Physics.
Sat, 01 Jan 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/957481994-01-01T00:00:00Z
- Experimental study of longitudinal end effects in transverse diffusion measurements of Na+ ion swarms in He gashttps://scholarbank.nus.edu.sg/handle/10635/96569Title: Experimental study of longitudinal end effects in transverse diffusion measurements of Na+ ion swarms in He gas
Authors: Tan, T.L.; Ong, P.P.; Hogan, M.J.
Abstract: The inevitable presence of longitudinal end effects in drift-tube mass spectrometers, if not corrected for, can cause significant systematic errors in measurements of ion transport coefficients. In our transverse diffusion measurements of Na+ ions in He and several other ion-neutral pairs, appreciable longitudinal end effects were detected for sufficiently high values of E÷N, the ratio of electric field to neutral gas number density. Systematic measurements at various drift length and analysis reveal that these end effects are generally more pronounced for ion-neural pairs with very low or very high mass ratio. They can be either positive or negative and their magnitudes can be quantified by a simple linear relationship of the transverse ion current density profile with drift length.
Sat, 01 Jan 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/965691994-01-01T00:00:00Z
- FTIR Spectrum of the ν2 Band of Deuterated Nitric-Acid (DNO3)https://scholarbank.nus.edu.sg/handle/10635/96683Title: FTIR Spectrum of the ν2 Band of Deuterated Nitric-Acid (DNO3)
Authors: Tan, T.L.; Looi, E.C.; Lua, K.T.; Maki, A.G.; Johns, J.W.C.; Noel, M.
Abstract: The infrared absorption spectrum of the ν2 band of deuterated nitric acid (DNO3) has been measured on a Bomem DA3.002 Fourier transform spectrometer in the wavenumber region 1640-1740 cm-1 with a resolution of 0.004 cm-1; 2036 transitions have been assigned in this hybrid type A and B band centered at 1688.3629 ± 0.0002 cm-1. The assigned transitions have been fitted to give nine rovibrational constants for the v2 = 1 state with a standard deviation of 0.00064 cm-1. The ratio of the transition moments, |μb/μa|, has been found to be 1.98 ± 0.10 for the band. © 1994 Academic Press. All rights reserved.
Fri, 01 Jul 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/966831994-07-01T00:00:00Z
- Line intensities in the ν8 band of HNO3https://scholarbank.nus.edu.sg/handle/10635/97066Title: Line intensities in the ν8 band of HNO3
Authors: Wang, W.F.; Looi, E.C.; Tan, T.L.; Ong, P.P.
Abstract: Line intensity measurements have been made on the v8 band of HNO3 using a high-resolution Fourier transform infrared spectrum in the region 739-800 cm-1. A least-squares fit of a total of 710 line intensities in the P and R branches was performed, leading to accurate determination of five dipole moment operator constants. By utilizing these constants, the observed line intensities are well reproduced with an average random error of 6% and the integrated band intensity is found to be 15.7 ± 0.9 cm-2 atm-1 at 296 K. © 1996 Academic Press, Inc.
Mon, 01 Jul 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/970661996-07-01T00:00:00Z
- High-resolution FTIR spectrum and rotational structure of the ν8 band of methylene chloridehttps://scholarbank.nus.edu.sg/handle/10635/96820Title: High-resolution FTIR spectrum and rotational structure of the ν8 band of methylene chloride
Authors: Wang, W.F.; Tan, T.L.; Tan, B.L.; Ong, P.P.
Abstract: The high-resolution Fourier-transform infrared spectrum of the ν8 band of methylene chloride (CH2Cl2) was measured in the range 1230-1305 cm-1. The band shows the typical A-type contour of an asymmetric-top molecule. A rovibrational structure analysis of the spectrum provided a set of accurate upper state constants up to some quartic centrifugal distortion constants which could reliably reproduce the observed spectrum. The absorption lines of the two isotopomers CH2 35Cl2 and CH2 35Cl37Cl were identified. A total of 1314 transitions for CH2 35Cl2 and 595 transitions for CH2 35Cl37Cl were assigned and fitted with an isotopic band center shift of about 0.035 cm-1 for this CH2 wagging fundamental mode. The measurement on the integrated band intensity was also performed and gave a value of (1.57 ± 0.08) × 10-17 cm/ molecule, taking into account the contribution from the hot bands in this region. Comparison between the observed and calculated band intensity gave an estimate of the dipole transition moment component along the a-axis at a value of |μa| = 0.218 D. © 1996 Academic Press, Inc.
Thu, 01 Feb 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/968201996-02-01T00:00:00Z