Vibrational Deactivation of HF(<i>v</i>=1) in Pure HF and in HF-Additive Mixtures

Abstract

The laser-excited vibrational fluorescence method has been used to obtain room temperature (294±2°K) vibrational relaxation rates for pure HF and in HF-additive mixtures. Measurement of the quenching of HF(v=1) fluorescence in HF–HF and HF-additive collisions has yielded the following total deactivation rates: HF†Ar&amp;lt;60 sec−1· torr−1, HF†N2=(1.25 ± 0.6) × 102 sec−1· torr−1, HF†D2=(3.7± 0.4)× 103sec−1· torr−1, HF†H2=(2.4 ± 0.3) × 104sec−1· torr−1, HF†CO2=(5.9± 0.2)× 104 sec−1· torr−1, and HF†H2O≈ HF†D2O=(4.1± 0.5)× 106 sec−1· torr−1. The self-relaxation rate for HF was found to be HF†HF=(8.74± 0.1)× 104 sec−1 torr−1 in dilute Ar mixtures and also with other additives. A slower rate (4.4± 0.3)× 104 sec−1· torr−1 has been measured in pure HF and is believed to indicate nonequilibrium of the rotational degrees of freedom during self-relaxation of HF. Observation of 4.3 μ fluorescence from CO2(00°1) and double exponential fluorescent decay from HF–H2 mixtures has led to the following rates for CO2(00°1) and H2(v=1) deactivation: CO2†HF=(5.3± 0.2)× 104 sec−1torr−1, and H2†HF=(6.3± 0.4)× 104 sec−1torr−1. The room temperature data are much faster than predicted from an extrapolation of the available high-temperature shock tube results. The equal, near gas kinetic rates found for HF relaxation by H2O and D2O suggest that strong chemical bonding forces may be responsible for the HF-water relaxation.