DOPPLER PROFILES AND FINE-STRUCTURE BRANCHING RATIOS OF O(P-3(J)) FROM PHOTODISSOCIATION OF CARBON-DIOXIDE AT 157 NM

The O(2p 3P(j)) (j = 2, 1, and 0) fragments produced in the 157 nm photodissociation of CO2 were detected by resonance-enhanced multiphoton ionization in a molecular beam. The Doppler profiles and fine-structure branching ratios were measured for the oxygen-atom photofragment in the 3P(j) states. The Doppler profiles were analyzed to give an anisotropy parameter of beta = 2.0 +/- 0.2 and an internal energy equivalent to 3.9 +/- 0.3 vibrational quanta of CO. The fine-structure populations were found to be 0.70 +/- 0.05, 0.16 +/- 0.03, and 0.14 +/- 0.03 (with error bars of +/- sigma) for j = 2, 1, and 0, respectively. A mechanism is proposed in which complex on the 1B2 surface undergoes intersystem crossing to the 3B2 surface. A phase-space model with a constraint on the impact parameter is shown to be consistent with the observed energy release. The nonstatistical fine-structure population could be caused by long-range interactions on the triplet surface. In a bulb experiment, O(3P) was produced by quenching of O(1D). The fine-structure populations of the resulting O(3P(j)) were 0.64 +/- 0.04, 0.25 +/- 0.04, and 0.11 +/- 0.04. This state distribution is consistent with a long-lived complex which decays to give statistical products.