Vibrational Deactivation of HF(v=1) in Pure HF and in HF-Additive Mixtures

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 $\mathrm{HF–HF}$ and HF‐additive collisions has yielded the following total deactivation rates: ${\mathrm{HF}}^{†}\mathrm{Ar}\text{<60\hspace{0.17em}}{\sec }^{\text{−1}}·{\mathrm{torr}}^{\text{−1}},{\mathrm{HF}}^{†}{\mathrm{N}}_2{\text{=(1.25 ± 0.6) × 10}}^2\hspace{0.17em}{\sec }^{\text{−1}}·{\mathrm{torr}}^{\text{−1}},{\mathrm{HF}}^{†}{\mathrm{D}}_2{\text{=(3.7± 0.4)× 10}}^3{\sec }^{\text{−1}}·{\mathrm{torr}}^{\text{−1}},{\mathrm{HF}}^{†}{\mathrm{H}}_2{\text{=(2.4 ± 0.3) × 10}}^4{\sec }^{\text{−1}}·{\mathrm{torr}}^{\text{−1}}\mathrm{,\hspace{0.17em}}{\mathrm{HF}}^{†}{\mathrm{CO}}_2{\text{=(5.9± 0.2)× 10}}^4\hspace{0.17em}{\sec }^{\text{−1}}·{\mathrm{torr}}^{\text{−1}}$ , and ${\mathrm{HF}}^{†}{\mathrm{H}}_2\mathrm{O}\approx {\mathrm{HF}}^{†}{\mathrm{D}}_2\mathrm{O}{\text{=(4.1± 0.5)× 10}}^6\hspace{0.17em}{\sec }^{\text{−1}}·{\mathrm{torr}}^{\text{−1}}$ . The self‐relaxation rate for HF was found to be ${\mathrm{HF}}^{†}\mathrm{HF}{\text{=(8.74± 0.1)× 10}}^4\hspace{0.17em}{\sec }^{\text{−1}}\hspace{0.17em}{\mathrm{torr}}^{\text{−1}}$ in dilute Ar mixtures and also with other additives. A slower rate ${\text{(4.4± 0.3)× 10}}^4\hspace{0.17em}{\sec }^{\text{−1}}·{\mathrm{torr}}^{\text{−1}}$ 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 ${\mathrm{HF–H}}_2$ mixtures has led to the following rates for CO₂(00°1) and H₂(v=1) deactivation: ${\mathrm{CO}}_2^{†}\mathrm{HF}{\text{=(5.3± 0.2)× 10}}^4\hspace{0.17em}{\sec }^{\text{−1}}{\mathrm{torr}}^{\text{−1}}$ , and ${\mathrm{H}}_2^{†}\mathrm{HF}{\text{=(6.3± 0.4)× 10}}^4\hspace{0.17em}{\sec }^{\text{−1}}{\mathrm{torr}}^{\text{−1}}.$ 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.