De-excitation of CO2(00°1) by Hydrogen Fluorides

Vibrational de-excitation of CO2(00°1) by HF and DF molecules is investigated on the basis of vibration-to-rotation energy transfer in the temperature range 300°–2000°K. The calculation shows that the vibrational relaxation is very fast in both CO2 (00°1) -HF and CO2(00°1)-DF collisions, and the results are in reasonable agreement with laser-excited fluorescence measurements around 350°K. For CO2 (0001) -HF, an inverse temperature dependence of the relaxation time is found between 300° and 400°K; the relaxation time at 360°K is about 30% longer than that at 300°K. For this system the relaxation times change from 0.023 μ sec·atm at 300°K to 0.0035 μsec· atm at 2000°K. No inverse temperature dependence is found for CO2 (0001) -DF. From a comparison with experimental data it is predicted that the deexcited-states of CO2 are (00°0) and (0110), respectively, for the CO2 (0001) -HF and CO2 (0001) -DF relaxation processes. The difference in the final states is explained in terms of the relative efficiency of HF and DF in de-exciting CO2(00°1). Throughout the calculation, the effects of translational motion and molecular attraction on relaxation processes are considered.