Vibrational relaxation of HF in the temperature range 600–2400 °K

Abstract

Hydrogen fluoride vibrational deactivation by HF, Ar, and F atoms has been studied in the temperature range 600–2400 °K using the shock tube-laser-induced fluorescence method. Mixtures of HF–Ar and F2–HF–Ar were heated by reflected shock waves; following establishment of thermal equilibrium, HF was vibrationally excited by pulsed radiation from an HF pin laser. Relaxation times were obtained from the time-resolved decay of the laser-induced vibrational fluorescence. Measurements of relaxation by F atoms were limited to temperatures > 1500 °K, where F2 dissociates completely behind the reflected shock wave. The HF self-relaxation time, p τHF–HF, exhibits a broad maximum with temperature, peaking at ≈ 0.10 μsec · atm near 1400 °K. Fluorine atoms were found to be 2–5 times more efficient than HF molecules for HF vibrational deactivation over the range 1500–2400 °K. Argon is a very inefficient collision partner; values of p τHF–Ar over the range 800–2400 °K are reported. This is the first study in which the maximum of pτHF–HF with temperature has been fully described; the present results both confirm and unify those of previous high (> 1400 °K) and low (< 1000 °K) temperature studies.