Resonent Vibration-Vibration Energy Transfer Between Vibrationally Excited HBr (X1Σ+ ν"=5) and H2, N2, CO2, and HBr

Collisional deactivation rate constants, k(5) (M) for HBr(X-1 Sigma(+) nu '' = 5) by M = H-2, N-2, CO2, and HBr were obtained using the degenerated stimulated hyper-Raman (OSHR) pumping method in a pumping-probe configuration. High-resolution transient laser induced fluorescence (LIF) was used to detect collisionally relaxed HBr. For M = CO2, an efficient near-resonant 1-1 vibration-to-vibration (V-V) energy exchange was observed. It appeared that the presence of a strong infrared-active vibrational mode was a favorable situation for an efficient V-V energy transfer. A 1-1 resonance exciting the infrared forbidden N-2 (1 <- 0) vibration was also observed, but it was 2 orders of magnitude smaller than that of CO2. Self-relaxation rate constants of HBr (nu '' = 5) were measured. Single quantum relaxation accounted for about 70% of the total relaxation out of state nu '' = 5, and two-quantum relaxation made contributions (25%) to the vibrational relaxation at this vibrational energy. Direct evidence for 2-1 resonance in HBr (nu '' = 5) + H-2 was observed. Initial preparation of HBr (nu '' = 5) resulted in nearly no population in HBr (nu '' = 4), but direct population of HBr (nu '' = 3). Therefore only 2-1 resonant energy transfer was important for H-2 relaxation. The state specific rate constant for HBr was obtained by the analysis of the state-to-state relaxation data. It was found that the data could be fitted with one adjustable normaligation parameter using a single-quantum relaxation model, which restricted the rate constant. A strong mass effect on the vibrational relaxation rate constant was observed. A further check of the character of the V-V resonant energy transfer in highly vibrationally excited HBr was the temperature dependence of the rate constants. For M = CO2, the temperature dependence of the 1-1 near-resonant energy transfer rate constats was found to be inverted. In contranst, the temperature dependence of the relaxation rate constants for M = H-2 and HBr was normal. For M = N-2, a weak but position temperature dependence was found. It suggested that this resonance occurred by a different mechanism compared with that in CO2.