Vibration–vibration energy transfer from H2(v= 1) and D2(v= 1) to selected diatomic and polyatomic hydrides and deuterides

Abstract

Rate constants have been measured for energy transfer from H₂(v= 1) and D₂(v= 1) to a variety of hydride and deuteride molecules. The H₂ or D₂ is excited by a stimulated Raman vibrational pumping technique and time-resolved infrared fluorescence is observed from the molecular collision partner. The following rate constants (k/10^–14 cm³ molecule^–1 s^–1) have been determined at 295 ± 5 K: H₂–HCl, 2.8₄± 0.14; H₂–HCN, 6.8 ± 0.2; H₂–C₂H₂, 7.8 ± 0.4; H₂–CH₄, 2.4 ± 0.3; H₂–C₂D₂, 0.56 ± 0.03; H₂–DCN, 0.39 ± 0.05; D₂–HBr, 13.3 ± 0.5; D₂–HCN, 1.12 ± 0.08; D₂–DCN, 3.1 ± 0.2. The results are consistent with vibration–vibration energy transfer from the homonuclear molecule to the collision partner with the discrepancy between the two vibrational transition energies being the single strongest factor in determining the probability of energy transfer. The rates of relaxation of the modes excited in the polyatomic molecules were too rapid to be measured directly in the present experiments. The relative rates of relaxation of HCN and C₂H₂ in similar gas mixtures with H₂ have been estimated by comparing the intensities of infrared fluorescence excited from these mixtures under identical conditions.