Vibrational relaxation of HBr (V = 1) state in methane, water, helium, and hydrogen gaseous mixtures

The rates of vibrational relaxation of HBr(V = 1) in CH₄, CD₄, H₂O, ³He, and HD mixtures have been measured by the laser‐excited vibrational fluorescence technique. The relaxation rates of ${\mathrm{HBr–}}^3\mathrm{He}$ and $\mathrm{HBr–HD}$ mixtures at 296 °K show cross sections of V→ T, R energy transfer as ${\sigma }_{{\mathrm{HBr–}}^3\mathrm{He}}{\text{=3.2± 0.2× 10}}^{\text{−21}}\hspace{0.17em}{\mathrm{cm}}^2$ , ${\sigma }_{\mathrm{HBr–HD}}{\text{=1.3± 0.1× 10}}^{\text{−20}}\hspace{0.17em}{\mathrm{cm}}^2$ . The rates of HBr in methane and water gaseous mixtures show ${\sigma }_{{\mathrm{HBr–CH}}_4}{\text{=6.4± 0.5× 10}}^{\text{−‐18}}\hspace{0.17em}{\mathrm{cm}}^2{\mathrm{;\hspace{0.17em}\sigma }}_{{\mathrm{HBr–CD}}_4}{\text{=4.6± 0.6× 10}}^{\text{−17}}\hspace{0.17em}{\mathrm{cm}}^2{\mathrm{;\hspace{0.17em}\sigma }}_{{\mathrm{HBr–H}}_2\mathrm{O}}{\text{=1.5± 0.2× 10}}^{\text{−18}}\hspace{0.17em}{\mathrm{cm}}^2$ . The predominance of vibration‐to‐vibration energy transfer, and not vibration‐to‐translation or rotation in HBr‐methane collisions, is suggested by the larger cross section of the deuterated compound collision. Comparison of the relative efficiencies of vibrational deactivation of HBr by collisions with hydrogen isotopes and helium isotopes reveals that intramolecular vibration‐to‐rotational energy transfer seems to be an important process involved.