Product distributions in the 157 nm photodissociation of CO₂

The vibrational and rotational distributions of CO(¹Σ _g⁺) produced in the 157 nm photodissociation of CO ₂ have been determined by measuring vacuum-ultraviolet laser-induced fluorescence spectra of the CO photoproduct. The photodissociation of CO ₂ is known to occur via two pathways; one yielding O(¹D) and the other yielding O(³P). Spin conservation and previous experimental studies confirm that dissociation via the O(¹D) channel is the dominant process. The available energy for this channel is sufficient to populate only the ground and first excited vibrational levels of CO. We measured the rotational distributions for CO in υ = 0 and υ = 1 and found them to be nonBoltzmann. In fact, a highly structured distribution with distinct peaks at J = 10,24,32, and 39 is observed for CO in υ = 0. A less structured population is displayed by molecules in υ = 1. The relative vibrational population (υ = 0/υ = 1) was determined to be 3.7 ± 1.2. Doppler spectra of individual rovibronic transitions were also recorded. The profiles have widths in accord with the available translational energy, display the expected v⊥J correlation, and are best described by an isotropic distribution of the velocity vectors with respect to the polarization direction of the dissociation light.