Near-resonant vibration↔ rotation energy transfer

A theory of $\mathrm{vibration}\to \mathrm{rotation}$ energy transfer, which takes specific account of near resonances between quantized vibrator and rotor energy levels, is derived. This theory is in good agreement with experimental data on the deactivation of ${\mathrm{BCl}}_3{\mathrm{(\nu }}_4\text{=1 Δ E=243}{\mathrm{cm}}^{\text{−1}})$ by HCl and DCl, and in fair agreement with data for BCl₃ with H₂, HD, and D₂. Theories that treat the rotor classically do not adequately predict these transition probabilities. The effect of using a first Born approximation is compared to a two‐level close‐coupled calculation, and the effect of a modified‐wave‐number approximation is examined; neither of these approximations materially affect the results. The P_HCl/P_DCl ratio is predicted to decrease from large values at low temperatures to nearly unity at higher temperatures.