Infrared photochemistry of ethylene clusters

Infrared irradiation of ethylene clusters formed in supersonic molecular beams, using a low power cw CO2 laser, results in the photodissociation of a large fraction of the van der Waals molecules. Under such conditions, infrared absorption intensity exhibits first-order power dependence and is readily detected as loss in molecular beam intensity. Intramolecular energy transfer rates, determined by measuring spectral linewidths, are shown to vary with the vibrational mode initially excited. Ethulene clsuters containing one quantum of vibrational energy corresponding to the νn7 fundamental in the monomer (949 cm-1) have a vibrationally predissociative lifetime of 0.33 psec. In comparison, the relaxation rate of ethulene-d4 clusters with one quantum of exctation corresponding to the ν12 (1078 cm-1) mode of C2D4 is 0.7 psec