COLLISIONAL RELAXATION OF TRANSLATIONAL ENERGY AND FINE-STRUCTURE LEVELS OF THE O(P-3(J)) ATOM CREATED IN THE PHOTODISSOCIATION OF SO2 AT 193 NM

Collision-induced energy transfer and intramultiplet relaxation processes of O(2p(4) P-3(j)) j=0, 1, and 2 have been studied, using a vacuum-ultraviolet laser-induced fluorescence technique. The O(P-3(j)) atoms are produced from the photodissociation of SO2 at 193 nm. Doppler profiles of the O(P-3(2)) 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(P-3(j)) atoms are thermalized at 300 K after a number of collisions with either He, Kr, Xe, N-2, or CO2. A Monte Carlo calculation using the hard-sphere collision model provides the cross sections for relaxation of the translational energy; 21+/-3 Angstrom(2) for He, 25+/-3 Angstrom(2) for Kr, and 25+/-5 Angstrom(2) 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 Angstrom(2) for Kr and 1.4+/-0.7 Angstrom(2) for Xe.