Infrared photodissociation of van der Waals molecules containing ethylene

Vibrational predissociation line shapes in the ν7 region of the ethylene spectrum are measured for van der Waals molecules of ethylene bound to Ne, Ar, Kr, C2H4, C2F4, and larger ethylene clusters. The predissociative rate is very fast for this group of molecules. The vibrationally excited state lifetimes are 0.44, 0.59 and 0.89×10−12 sec for (C2H4)2, Ar⋅C2H4, and C2H4⋅C2F4 respectively. That the observed line shapes are homogeneous is demonstrated by the fact that a low-power, narrow frequency bandwidth laser can dissociate a large fraction of the initial ensemble of ethylene clusters. The observed transition probability is proportional to the number of ethylene subunits for clusters containing three or fewer ethylene subunits. These observations are interpreted in terms of intramolecular energy flow directly from ethylene ν7 to the weak van der Waals modes of motion.