Vibration-translation and vibration-rotation energy transfer in polyatomic molecules

Abstract

The published ultrasonic measurements of vibrational relaxation at 300 K for polyatomic molecules possessing fundamental modes of frequency [graphic omitted] 1200 cm^–1 can be fitted to two linear plots of log₁₀Z₁₀ against v_min(the lowest fundamental frequency): (I) for molecules containing hydrogen; (II)(much lower efficiency) for all other molecules. The inference is drawn that, within each group, the overlap of translational wave functions is the only important factor in energy transfer, so that P₁₀(= 1/Z₁₀)= exp(–XΔE_int), where ΔE_int is the amount of internal energy transferred to translation. Systematic small deviations from plot (I) can be explained on the assumption that vibrational transitions are accompanied by simultaneous small rotational transitions, and that ΔE_int=ΔE_vib+ΔE_rot. This effect is not large enough to account for the difference between groups (I) and (II), which is attributed to the large physical amplitude of vibrations involving hydrogen atoms. Tables are given of vibrational relaxation times and collision numbers for 75 gases.