Vibrational Deactivation Of CO Research Articles

Experimental Investigation of Vibrational Deactivation of CO Molecules in a Supersonic Gas Flow

The vibrational temperature and vibrational deactivation time of CO molecules in collisions with hydrogen atoms are measured using the broadband version of the coherent anti-Stokes Raman scattering technique (CARS). Carbon monoxide with hydrogen-containing admixtures (H2, H2O) heated in a reflected shock wave up to temperatures 2900–5100 K escaped through a supersonic wedge-shaped nozzle. The measurements demonstrate the high efficiency of hydrogen atoms in the vibrational deactivation of CO. A difference in the measured temperature dependences of the vibrational excitation and deactivation times of CO molecules in collisions with H atoms, which seems to be associated with a difference in the mechanisms of CO-H complex formation, is noted.

A new He–CO interaction energy surface with vibrational coordinate dependence. II. The vibrational deactivation of CO(v=1) by inelastic collisions with He3 and He4

Vibrational relaxation cross-sections and rate constants have been calculated for the deactivation of CO(v=1) by He3 and He4 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.

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<T<300 K. The CO rotation is treated using the infinite-order sudden (IOS) approximation, while the rotation of H2 is included using the coupled states (CS) approximation. A near-resonant energy transfer process, in which the H2 molecule is rotationally excited from J=2 to J=6 on relaxation of CO(v=1), is found to account for the experimental observation that kCO–pH2/kCO–oH2>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−1, the relaxation cross sections increase at a rate which is insufficient to account for the observed upturn in the experimentally determined deactivation rate constants for the CO–nH2 system below 60 K. Rate constants for the deactivation of CO(v=1) by oD2 and pD2 have also been calculated and compared with experimental data.

Time-resolved infrared fluorescence studies of the collisional deactivation of CO2(0001) by large polyatomic molecules

Abstract The time-resolved infrared fluorescence (IRF) technique has been used to study the vibrational deactivation of CO 2 (00 0 1) by large polyatomic molecules at ambient temperature (295 ± 2 K).The excited CO 2 molecules were prepared by direct pumping with the P(21) line of a pulsed CO 2 laser at 10.6 μm. The bimolecular rate constant for deactivation by CO 2 was determined to be (0.353 ± 0.026) × 10 3 Torr −1 s −1 , in excellent agreement with previous work. The rate constants for deactivation by the large polyatomic molecules, c-C 6 H 10 , c-C 6 H 12 , C 6 H 6 , C 6 D 6 , C 7 H 8 , C 7 D 8 , C 6 H 5 F, p -C 6 H 4 F 2 , C 6 HF 5 and C 6 F 6 , were found to be (143 ± 18), (150 ± 12), (120 ± 4), (238 ± 9), (140 ± 5), (234 ± 15), (121 ± 7), (132 ± 23), (132 ± 12), and (94 ± 5) × 10 3 Torr −1 s −1 , respectively. Experimental deactivation probabilities and average energies removed per collision are calculated and compared. There is little difference in deactivation probabilities between the acyclic ring compounds and their aromatic analogues but the perfluorinated compound, C 6 F 6 is clearly less efficient than its hydrocarbon analogue, C 6 H 6 . The perdeuterated species, C 6 D 6 and C 7 D 8 show considerably enhanced deactivation relative to the other species, probably as a result of near-resonant intermolecular V-V energy transfer.

Vibrational deactivation of CO ( ν = 1) by inelastic collisions with 3He and 4He at low impact energies

Vibrational relaxation cross sections are calculated within the coupled-states approximation for COHe systems. Resonant structure in the cross sections is observed close to the vibrational threshold, and attributed to the formation of quasi-bound states due to the attractive part of the interaction potential. The contribution of these resonances to low-temperature vibrational relaxation rate constants is considered.

Vibrational deactivation of CO( v = 1) by p-H 2. The importance of the higher-order multipole moments

Detailed calculations show that the agreement with the experimental rate constant for the vibrational deactivation of CO by p-H 2 is improved by including the octopole moment and the hexadecapole moment of CO. Previous calculations included only the dipole and the quadrupole moments. The present theoretical rates are 10–30 percent lower than the experimental values.

Vibrational deactivation of CO(υ = 1) by p-H 2 and o-H 2

Detailed rate constants are calculated for the vibrational deactivation of CO(υ = 1) in collisions with H 2(υ = 0, j = 0, 1 or 2). which simultaneously undergoes the rotational transitions Δ j = 0, 2 or 4. Results for n-H 2 agree well with experiment from 200 to 2000 K, the theoretical results are 35% lower than the experimental values at 100 K. The deactivation is faster in collisions with p-H 2 than o-H 2 from 100 to 500 K due to the near-resonance process CO(υ = 1) + H 2( j = 2) → CO(0) + H 2(6).Δ E = −83.3 cm −1. This process is induced by the interaction between the H 2 hexadecapole and the CO multipoles. The pure V-T energy transfer dominates above 500 K- The potential includes a short-range fit to recent SCF calculations. the multipole interaction and the dispersion. The vibration of CO and the vibration and rotation of H 2 are treated quantum mechanically. Classical mechanics is used for the rotation of CO and for the relative translation.

Vibrational relaxation of CF4 and CH4 and energy transfer between these gases and CO

Measurements have been made of the rates of vibrational relaxation of CF4 and of CH4 in the temperature range 400–700 K using a shock tube.Below 600 K the equilibrium population of CO in the (v= 1) state is very small and it is possible to measure the rates of the (VT) excitation of CF4 and of CH4 by CO. Rate constants have been determined for these processes in the temperature range 400–450 K.Above temperatures of 750 K it is possible to measure the rates for the vibrational excitation of CO by vibrationally excited CF4, or by vibrationally excited CH4. Data are given for these processes in the temperature range 750–1500 K and comparisons are made with laser fluorescence data at lower temperatures on the vibrational deactivation of CO by CF4 and by CH4.

Vibrational deactivation of CO(v=1) by oxygen atoms

Collisional relaxation of vibrationally excited carbon monoxide (v=1) by oxygen atoms has been measured from 265 to 389 °K using the laser induced fluorescence technique. Atom concentrations were measured with an ESR spectrometer. The measured rates, which vary from 7.5(+9.4−7.5) 102 sec−1 torr−1 at 265 °K to 4.2±2.0 103 sec−1 torr−1 at 389 °K show good agreement with existing high temperature shock tube results on a Landau–Teller plot. These rates indicate that atomic oxygen may be the dominant quenching species in many carbon monoxide chemical lasers.

The vibrational deactivation of CO (ν = 1)_by O 2 measured between 300 and 80 K

Laser fluorescence measurements of the CO/O 2 vibration-vibration (VV) exchange rate have been performed between 300 and 80 K. The results show a temperature dependence similar to the observed from (VT) processes at low temperatures.

Vibrational deactivation of CO by n-D 2 and o-D 2 measured between 340 K and 110 K using laser fluorescence

Vibration to vibration and rotation (VVR) exchange occurs between CO and D 2 over the temperature range 340 K to 230 K, whilst at lower temperatures VT deactivation is dominant. Probabilities for these processes and for D 2D 2 deactivation are presented

Temperature-dependent relaxation of CO(v=1) by HD, D2, and He and of D2(v=1) by D2

Rate constants for the vibrational deactivation of CO in collisions with HD, D2, and He have been measured as a function of temperature using the laser excited vibrational fluorescence technique. Throughout the 109–630 °K range, CO–He and CO–HD samples exhibit a single exponential decay, dominated by V–T,R transfer, with rates increasing rapidly with temperature. Typical collision deactivation rate constants at 630 °K are 22.7 sec−1 torr−1 for He and 82.5 sec−1 torr−1 for HD, and, at 109 °K, 0.067 sec−1 torr−1 for He and 0.27 sec−1 torr−1 for HD. At low temperatures, diffusion and radiative decay become important contributions to the observed rates. In CO–D2 mixtures, double exponential decay of CO fluorescence at large D2 mole fractions is obtained, corresponding to rapid V–V transfer between the (v=1) vibrational levels of CO and D2, followed by coupled V–T,R deactivation. The V–V transfer rate (ΔE=−850 cm−1) increases from 0.26 sec−1 torr−1 at 202 °K to 69.4 sec−1 torr−1 at 633 °K. The V–T,R deactivation rate constant for excited CO by D2 is significantly slower than that by HD and H2, going from 0.089 sec−1 torr−1 at 156 °K to 3.7 sec−1 torr−1 at 450 °K, indicating the decreased importance of the rotational states of D2 in the deactivation of CO than hypothesized for H2 and HD. The deactivation of excited D2 by collisions with D2 also increases with temperature, ranging from 0.080 sec−1 torr−1 at 202 °K to 6.9 sec−1 torr−1 at 450 °K.

Vibrational deactivation of CO by n-H 2, by p-H 2 and by HD measured down to 77 K using laser fluorescence

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.

Vibrational deactivation of CO2(3Σ) by collisions with atoms

Vibrational deactivation of CO₂(³Σ) by collisions with atoms

Vibrational deactivation of CO 2(00°1) molecules by ONF, COF 2 and O 3

Measurements have been performed with the laser excited fluorescence method of the rates of vibrational deactivation of the upper CO 2 laser level by ONF, COF 2 and O 3. In each case, rapid near-resonant V → V transfer deactivation mechanisms are indicated.