Measurement of vibrational-vibrational exchange rates for excited vibrational levels (2≤v≤4) in hydrogen fluoride gas

A measurement of the total decay rate (due to both V-V and V-T processes) of the second, third, and fourth vibrational levels in vibrationally cold hydrogen fluoride gas is described. The measured endothermic rate constants are 8×105, 1.6×106, and 1.4×106 sec−1 · torr−1, respectively. It is argued that the major contribution of each of these decay rates is from the process HF(ν = n)+HF(ν = 0)→ HF(ν = n − 1) + HF(ν = 1) where n = 2,3, and 4. The technique used in these measurements is a novel variation of the method of laser induced fluorescence. It involves exciting the first; first and second; or first, second, and third vibrational levels of HF via multiband laser optical pumping. Collisional population of the level of interest then occurs through the reverse of the above vibrational exchange process. An analysis using rate equations shows that the rise rate of the population of a given level is governed by the forward rate of the above process. It is also shown theoretically and experimentally that in ...

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