THE 193-NM PHOTODISSOCIATION OF CYCLOBUTANONE - DYNAMICS OF THE C2 AND C3 CHANNELS

The 193-nm photolysis of cyclobutanone has been investigated by obtaining vacuum-ultraviolet laser-induced fluorescence spectra of the CO photoproduct. The rotational distribution in each vibrational level (v″ = 0-3) was fit well by a sum of two Boltzmann distributions with average temperatures Tlow ∼ 200 K and Thigh ∼ 3000 K. The high-temperature component comprised ∼85% of the total CO yield, independent of vibrational level. The vibrational distribution was also thermal, corresponding to a temperature of 2560 ± 100 K. Doppler profiles of individual rovibronic transitions were fit by Gaussian line shapes corresponding to an average translational temperature of ∼2500 K. The two rotational distributions were assigned to CO produced via two reaction pathways. The vibrational, rotational, and translational distributions for the high-temperature channel were found to be consistent with the distributions predicted by a statistical prior calculation for dissociation of cyclobutanone to CO and cyclopropane, the C3 channel. The low-temperature channel was assigned to CO resulting from unimolecular decomposition of an excited ketene product, the C2 channel. Statistical prior calculations for the ketene plus ethylene channel indicate that only electronically excited ketene should be sufficiently energetic to dissociate to CO and methylene. © 1990 American Chemical Society.