Vibrational Energy Transfer Processes in Shock-Heated Binary Gas Mixtures of CO with CO2, N2O, and COS

The vibrational relaxation rates of binary mixtures of CO with the additives CO₂, N₂O and COS have been measured in incident shock waves over a temperature range 1200–2000°K. The fundamental vibration of CO was found to be closely coupled to the asymmetric stretching vibration in each additive and so the rate determining step was not V‐V energy exchange between CO and the additive, but intramolecular energy transfer within the polyatomic species. For CO/CO₂ this step is $${\mathrm{CO}}_2\text{(001)+}\mathrm{CO}{\displaystyle {lim}^{{\mathrm{\to k}}_4}}{\mathrm{CO}}_2{\mathrm{(\nu }}_2{\mathrm{/\nu }}_1\mathrm{)+}\mathrm{CO},$$ where the forward rate constant is given by $$\mathrm{CO}({\mathrm{CO}}_2\mathrm{)\hspace{0.17em}}{\log }_{10}{\mathrm{(k}}_4/{\mathrm{atm}}^{\text{−1}}·{\sec }^{\text{−1}}{\text{)=8.69–28.1\hspace{0.17em}T}}^{\text{−1/3}}.$$ For the other additives the rate constants for the analogous reactions are given by $$\mathrm{CO}({\mathrm{N}}_2\mathrm{O}\mathrm{)\hspace{0.17em}}{\log }_{10}{\mathrm{(k}}_4/{\mathrm{atm}}^{\text{−1}}·{\sec }^{\text{−1}}{\text{)=8.50–23.6\hspace{0.17em}T}}^{\text{−1/3}}$$ $$\mathrm{CO}(\mathrm{COS}\mathrm{)\hspace{0.17em}}{\log }_{10}{\mathrm{(k}}_4/{\mathrm{atm}}^{\text{−1}}·{\sec }^{\text{−1}}{\text{)=7.56–8.40\hspace{0.17em}T}}^{\text{−1/3}}.$$ These results are in accord with those from recent laser fluorescence measurements and can be reconciled with shock measurements on other systems.