Excimer laser photolysis studies of translational-to-vibrational energy transfer in collisions of H and D atoms with CO

Abstract

Translational-to-vibrational excitation of carbon monoxide is observed as a result of collisions of high energy H and D atoms with CO. The fast atoms are produced by excimer laser photolysis of H2S, D2,S, HCl, HBr, or HI at 193 or 248 nm. Detection of time and wavelength-resolved infrared fluorescence is used to quantify the CO vibrational state excitation. The CO (v=1−6) state distribution from H (H2S, 193 nm, Ecm=2.3 eV) +CO collisons is 0.74±0.15, 0.15±0.01, 0.08±0.01, 0.01±0.01, 0.02±0.01, and 0.01±0.01. The corresponding state distribution from D (D2S, 193 nm, Ecm=2.2 eV)+CO is 0.79±0.19, 0.13±0.01, 0.05±0.02, 0.02±0.02, 0.01±0.01, and 0.01±0.01. Rotational excitation is at least as significant as vibrational excitation, based on estimates of the total energy transfer. Measurements of the relative vibrational excitation efficiency as a function of initial H atom energy show that the fraction of translational energy converted to CO vibration increases by more than 300% as the initial H atom energy is increased from 1.0 to 3.2 eV. Good qualitative agreement is found between the experimental results and classical trajectory calculations carried out for collinear collisions of H and D atoms with CO using a simple repulsive interaction potential.