Diode laser probe of CO2 vibrational excitation produced by collisions with hot deuterium atoms from the 193 nm excimer laser photolysis D2S

The 193 nm excimer laser photolysis of D₂S in D₂S/CO₂ mixtures produces fast deuterium atoms (E_TR∼2.2 eV) which vibrationally excite CO₂ molecules via inelastic translation-vibration/rotation (T-V/R) energy exchange processes. A high resolution (10^-3 cm^-1) cw diode laser probe was used to monitor the excitation of ν₃ (antisymmetric stretch) and ν₂ (bend) vibrations in CO₂. The present results are compared with previous experiments involving hot hydrogen atom excitation of CO₂ in H₂S/CO₂ mixtures as well as with theoretical calculations of the excitation probability. The probability for excitation of a ν₃ quantum in CO₂ is about 1%-2% per gas kinetic D/CO₂ collision. Bending (ν₂) quanta are produced about eight times more efficiently than antisymmetric stretching (ν₃) quanta. The thermalization rate for cooling hot D atoms below the threshold for production of a ν₃ vibrational quantum corresponds to less than 2 D*/D₂S collisions or 15 D*/CO₂ collisions.