DYNAMICS OF ACETALDEHYDE DISSOCIATION AT 308 NM - ROTATIONAL (N, K-A)AND TRANSLATIONAL DISTRIBUTIONS OF THE HCO PHOTOPRODUCT

The photodissociation dynamics of acetaldehyde excited at 308 nm and p roducing CH3 and HCO fragments have been explored. A detailed analysis of the nascent HCO rotational distribution, including the distributio n over different Nand K-a states, reveals a distribution that is reaso nably characterized by a Boltzmann temperature of 570 +/- 50 K and the refore an average rotational energy of 7.1 +/- 0.5 kJ/mol. No strong p reference for HCO in different K-a states was observed. An average tra nslational energy of 11 +/- 2 kJ/mol was measured from Doppler broaden ing of the rotational lines, from which was inferred a CH3 translation al energy of 21 +/- 4 kJ/mol. The available energy of 39 kJ/mol theref ore dictates that little or no energy remains to be partitioned into t he internal energy of the methyl fragment. The distribution of energy in the fragments is nonstatistical but well-represented by a simple im pulsive description of the process with a late barrier which inhibits coupling of the impulse into vibrations of the fragments.