The deactivation of HF(v = 3) by water

Water is often present as an impurity in HF chemical laser systems and can affect laser performance because of the large HF(1) - H2O deactivation rate coefficient. Diatomic molecules have been found to deactivate the higher vibrational levels of HF(v) with rate coefficients that scale with v as v superscript n where n = 2.7 when the deactivation process is exothermic. This scaling does not hold for HF(v) - H2 collisions in which the primary deactivation process is an endothermic V-V transfer with the endothermicity increasing with v. The room temperature (T = 295 K) deactivation rate of HF (v = 3) by H2O has been measured to be faster than the deactivation rate of HF(v = 1) by H2O by a factor of 3.9. On the basis of a previously reported measurement of the HF(v = 1) - H2O rate coefficient, the deactivation rate coefficient of HF(v = 3) by H2O is estimated to be 16 microseconds/Torr, which is a factor of 3 faster than the hard sphere collision rate. The theoretical implication of this fast-rate coefficient are reviewed.