C.J.S.M. Simpson

The measurement of rate constants for the vibrational deactivation of 12C16O by H2, D2 and 4He in the gas phase down to 35 K

Abstract Rate constants for the vibrational deactivation of 12 C 16 O by H 2 , D 2 and 4 He have been determined by laser-induced fluorescence in the gas phase at low temperatures. The rate constants for 12 C 16 O(ν=1)H 2 and 12 C 16 O(ν=1)D 2 have been measured down to 35 K and those for 12 C 16 O(ν=1) 4 He have been measured to 40 K. This extension of our previous data has been made possible by the adoption of a frequency-doubled CO 2 laser. The rate constants for 12 C 16 O(ν=1)H 2 and 12 C 16 O(ν=1)D 2 show a minimum at 50 K, whereas that for 12 C 16 O(ν=1) 4 He steadily decreases with lowering temperature throughout the range studied here.

Vibrational deactivation of the bending mode of CO2 measured between 1500 K and 150 K

Abstract Energy transfer between vibrationally excited CO and CO 2 has been used to excite the bending mode of CO 2 . The rate of deactivation of this mode by CO 2 and by Ar has been measured down to 150 K.

Vibrational deactivation of CO by n-H2, by p-H2 and by HD measured down to 77 K using laser fluorescence

Abstract Probabilities for the (VT) and (VR) deactivation of CO have been calculated from relaxation times measured down to 77 K using laser fluorescence. Only in the case of deactivation by p -H 2 is the (VR) process important; its rate exceeds that for (VT) deactivation between 320 K and 110 K.

A new He–CO interaction energy surface with vibrational coordinate dependence. II. The vibrational deactivation of CO(v=1) by inelastic collisions with 3He and 4He

Vibrational relaxation cross-sections and rate constants have been calculated for the deactivation of CO(v=1) by 3He and 4He on a new intermolecular potential with vibrational coordinate dependence [T. G. A. Heijmen, R. Moszynski, P. E. S. Wormer and Ad van der Avoird, J. Chem. Phys. 107, 9921 (1997)]. The new surface is found to resolve the qualitative discrepancy between theory and experiment which existed in earlier theoretical calculations. The low impact energy regime has also been investigated focussing in particular on impact energies of less than 15 cm−1 above the vibrational (v=1) threshold. Resonance structure has been found to occur and a comparison is made with an earlier investigation of the low temperature region.

Vibrational relaxation of CO (v=1) by inelastic collisions with 3He and 4He

Calculations of the vibrational relaxation rate constants of the CO–3He and CO–4He systems are extended to lower temperatures than in any previous calculation and a comparison made with new experimental results in the temperature range 35–295 K for CO–3He and previously published results in the range 35–2300 K for CO–4He. Both the coupled states (CS) and infinite‐order sudden (IOS) approximations are used, with the self‐consistent‐field configuration interaction CO–He interaction potential of Diercksen and co‐workers. The CS approximation is found to give a similar level of agreement with experiment for the two isotopic species, while the performance of the IOS approximation is system dependent. The discrepancy between experimental and theoretical IOS rate constants is quite different for collisions involving 3He and 4He, so that it is not profitable to compare IOS results directly with experiment for these two systems at temperatures below 300 K. The differences between the measured and the CS calculated...

Vibrational relaxation of CO by H2 down to 73 K using a chemical CO laser

Abstract Laser fluorescent studies of CO relaxation have been made using a chemical CO laser. The results are compared with those obtained by other methods and the temperature range extended from 100 K to 73 K.

Vibrational deactivation of N2(v=1) by inelastic collisions with He3 and He4: An experimental and a theoretical study

A new N2–He intermolecular potential with vibrational coordinate dependence is presented. Rate constants for the vibrational deactivation of N2(v=1) by He in the gas phase have been calculated over the temperature range 5–300 K. Accurate values of the rate constants for this process are known down to 100 K. We have now extended these measurements down to 70 K for the deactivation of 14N2(v=1) by 4He and down to 50 K for the deactivation of 15N2(v=1) by 3He. Agreement between the theoretically calculated and the experimentally determined rate constants is excellent with the calculated values reproducing the experimental measurements within their error bars. An investigation of the low impact energy regime is also presented. While this focuses on collision energies of less than 20 cm−1 and yields rate constants which are in a temperature region inaccessible to our experimental method, it gives further insights into the influence of the attractive well on vibrational energy transfer processes.

The vibrational deactivation of CO(v=1) by inelastic collisions with H2 and D2

Calculations of the relaxation rate constants, kCO–H2, for the vibrational deactivation of CO(v=1) by pH2 and oH2 are reported in the temperature range 30 K 1 for this system at temperatures above 80 K. Evidence is presented to suggest that below this temperature, which represents the current lower limit of existing experimental data for the CO(v=1)-pH2 system, thermal depopulation of the J=2 rotational state in pH2 reduces the importance of the near-resonant energy transfer process in the determination of kCO–pH2. For T≪80 K the ratio kCO–pH2/kCO–oH2<1 is predicted on the basis of these calculations. At impact energies less than 60 cm...

Coupled cluster ab initio potential energy surfaces for CO...He and CO...H-2

Ab initio potential energy surfaces including the vibrational coordinate dependence are presented for CO… He and CO… H2 using the coupled cluster method with Brueckner orbitals. The interaction energy is calculated using the supermolecule approach. The calculation of rate constants for the vibrational relaxation of CO(v = 1) by He and their comparison with the experimentally measured values over the temperature range 40–300 K is used to test the accuracy of the CO… He surface. Comparison with results from an earlier surface calculated by symmetry adapted perturbation theory shows that the two surfaces have similar scattering characteristics and reproduce the experimental measurements to a similar level of accuracy. The potential surface for the CO… H2 system is presented as raw data in anticipation of future calculations.

The vibrational deactivation of the bending mode of CO2 by O2 and by N2

Shock tube measurements made between 1 500 and 350 K suggest that O2 is slightly more efficient at deactivating the bending mode of CO2 than is N2. The rate constant for its deactivation by air at 210 K has been estimated.