Shock-Tube Studies of HF Vibrational Relaxation

The vibrational relaxation of HF has been studied behind incident shock waves in the temperature range 1350–4000°K by monitoring the 2.7_−μ infrared emission. Relaxation times reduced to standard pressure were obtained for mixtures containing 1%–10% HF in argon and for mixtures containing N₂, He, and D₂. These data were used to calculate the relaxation times of HF due to these various gases. The relaxation times can be summarized by the expressions ${\mathrm{P\tau }}_{\mathrm{HF}‐\mathrm{HF}}{\text{=1.02×10}}^{\text{−2}}\hspace{0.17em}\exp {\text{(34.39/T}}^{\text{1/3}}\mathrm{)\hspace{0.17em}\mu }\sec ·\mathrm{atm}{\mathrm{,\hspace{0.17em}P\tau }}_{\mathrm{HF}‐\mathrm{Ar}}{\text{=1.62×10}}^{\text{−3}}\hspace{0.17em}\exp {\text{(111.97/T}}^{\text{1/3}}\mathrm{)\hspace{0.17em}\mu }\sec ·\mathrm{atm}{\mathrm{,\hspace{0.17em}P\tau }}_{\mathrm{HF}‐\mathrm{He}}{\text{=1.52×10}}^{\text{−4}}\hspace{0.17em}\exp {\text{(133.3/T}}^{\text{1/2}}\mathrm{)\hspace{0.17em}\mu }\sec ·\mathrm{atm}$ , and ${\mathrm{P\tau }}_{\mathrm{HF}‐{\mathrm{D}}_2}{\text{=5.1×10}}^{\text{−4}}\hspace{0.17em}\exp {\text{(96.6/T}}^{\text{1/3}}\mathrm{)\hspace{0.17em}\mu }\sec ·\mathrm{atm}$ . The values of ${\mathrm{P\tau }}_{\mathrm{HF}‐{\mathrm{N}}_2}$ fell between those for helium and deuterium. The relaxation time of HF due to itself is compared to the predictions of several theories of $\mathrm{V‐T}$ and $\mathrm{V‐R}$ energy transfer, and to published experimental data for other hydrogen halides. The HF rates of this study, together with the measured rate at room temperature, suggest the possibility of an attractive potential playing a dominant role in energy transfer at low temperature.