Vibrational energy disposal in reactive and inelastic collisions of H(D)+HCl(DCl) at 1–3 eV

Abstract

Vibrational energy disposal due to reactive exchange and unreactive translational-to-vibrational excitation in hyperthermal collisions of H+HCl and deuterated analogs is investigated by the excimer laser photolysis/infrared fluorescence technique. In the H+DCl system the excitation of DCl vibration increases from an energy efficiency of 4% to 9% as the initial H atom energy is increased from 1.4 to 3.1 eV. Only about 2% of the available energy appears as HCl vibration via H atom exchange, independent of the initial energy. The exchange reaction barrier is determined to be less than 0.95 eV (22 kcal/mol). At 2.3 eV collision energy the vibrational distribution of the HCl exchange product is relatively hot, with about 86% of the vibrational energy in molecules with v≥2. In the H+HCl system, where only the sum of inelastic and reactive collisions can be observed, the HCl vibrational distribution is markedly cooler, with only 60% of the vibrational energy in molecules with v≥2. The overall vibrational excitation efficiency of H+HCl is also a sensitive function of energy, increasing from 3% to 18% over the range 0.95 to 3.1 eV. This is consistent with an interpretation that the inelastic T–V excitation pathway is predominant. No information is obtained on the H atom abstraction channel.