Vibrational energy transfer from levels below 410 cm ^-1 in S₁ p-difluorobenzene. III. : Different propensity rules for polyatomic partners

Collision-induced vibrational energy transfer has been studied from three levels [30² (E_vib=240 cm^-1), 8² (E_vib=361 cm^-1), and 61 (E_vib=410 cm^-1)] in S₁ p-difluorobenzene (pDFB) in a supersonic free jet expansion using the polyatomic partners methane, ethane, cyclopropane, and i-butane. The data indicate that vibration-to-vibration transfer is not efficient. Nevertheless, significant differences are found to exist between the state-to-state branching ratios for the polyatomic partners and those observed previously for monatomic and diatomic partners, with the exception of nitrogen. For the polyatomic partners single quantum changes in low frequency modes are no longer dominant. The polyatomic partners generally display a preference for transfer via channels involving large pDFB vibrational energy loss. There are similarities in the preferred two quanta channels for polyatomic and diatomic partners.