Temperature dependence of V-V and V-R, T energy transfer measurements in mixtures containing HF

Abstract

A pulsed HF chemical laser has been used to excite HF molecules to their first vibrational level. The decay times of the infrared fluorescence from HF(ν = 1) have been used to determine the rate coefficients for energy transfer from HF to various collision partners including H2, D2, N2, O2, DF, HCl, CO2, NO, CO, and HBr. The experiments were performed at temperatures from 450 to 1000°K for most of the molecules. as well as at 295°K. For the higher temperature measurements, the experiments were performed behind a reflected shock wave in a shock tube. The compression heating capability of a shock tube has been used successfully as an alternative to a heated cell for laser-induced fluorescence measurements. The room-temperature probabilities of energy transfer from HF to the various molecules plotted versus energy mismatch fell along two distinct lines: one for homonuclear and one for heteronuclear molecules. The rate coefficients (cubic centimeters per mole second) for the molecules with the smallest energy mismatch had temperature dependences between T−1 and T0 near T = 295°K, while the molecules with larger energy mismatches and correspondingly smaller rate coefficients showed positive temperature dependences. The room-temperature relaxation rates of HF in the presence of the various molecules were measured to be H2, (1.7 ± 0.1) × 10−2; HCl, (1.7 ± 0.1) × 10−2; DF, (7.7 ± 0.4) × 10−2; CO2, (3.6 ± 0.2) × 10−2; D2, (3.1 ± 0.6) × 10−3; N2, (1.52 ± 0.15) × 10−4; O2, (4.5 ± 0.6) × 10−5; CO, (1.8 ± 0.2) × 10−3; HBr, (7.5 ± 1.0) × 10−3: and NO, (6.0 ± 1.0) × 10−3, in units of (μsec torr)−1. These rates represent the total relaxation rate of HF due to both V - V and V - R,T energy transfer. Relaxation rates of some of the chaperone molecules by HF as well as their self-relaxation rates were also measured.