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 τ_HF–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 τ_HF–Ar over the range 800–2400 °K are reported. This is the first study in which the maximum of pτ_HF–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.