Collisional relaxation of translational energy and fine-structure levels of the O(3P j) atom created in the photodissociation of SO2 at 193 nm

Abstract

Collision-induced energy transfer and intramultiplet relaxation processes of O(2p4 3Pj) j=0, 1, and 2 have been studied, using a vacuum-ultraviolet laser-induced fluorescence technique. The O(3Pj) atoms are produced from the photodissociation of SO2 at 193 nm. Doppler profiles of the O(3P2) atoms have been measured as a function of time delay between pump and probe laser pulses. The translational energy and j-level population of the O(3Pj) atoms are thermalized at 300 K after a number of collisions with either He, Kr, Xe, N2, or CO2. A Monte Carlo calculation using the hard-sphere collision model provides the cross sections for relaxation of the translational energy; 21±3 Å2 for He, 25±3 Å2 for Kr, and 25±5 Å2 for Xe. Assuming the principle of detailed balancing among the j levels, the cross sections for the collision-induced intramultiplet transition over the collision energy range 1–6 kcal mol−1 are obtained from the time evolution of the j-level populations: cross sections for the j=2→1 transition are 2.4±1.2 Å2 for Kr and 1.4±0.7 Å2 for Xe.