State-to-state dynamics of molecular energy transfer. Annual performance report, April 1, 1993--March 31, 1994

Abstract

During this budget period we have focussed our efforts toward completing experimental measurements of differential cross sections for fully-resolved state-to-state angular momentum transfer in NO + Ar collisions, including both the electronically adiabatic and nonadiabatic channels represented by: NO({sup 2}P{sub 1/2}, {nu} = 0,j = 1/2) + Ar {yields} NO({sup 2}P{sub l/2}, {nu} = 0,j{prime}) + Ar and NO({sup 2}P{sub 1/2}, {nu} = 0,j = 1/2) + Ar {yields} NO({sup 2}P{sub 3/2}, {nu} = 0,j{prime}) + Ar. We have also begun measurements of integral cross sections as a function of collision energy for state-resolved rotational excitation of the first triatomic molecule to be examined by this technique, in the system SO{sub 2} + He. Concurrently, we have also carried out collision experiments in the system SO{sub 2} + He. These are the first crossed molecular beam experiments on state-resolved rotational energy transfer of a triatomic molecule. State-to-state integral cross sections have been measured as a function of final rotational state at a fixed collision energy of 473 cm{sup {minus}1}, and as a function of collision energy for six selected final rotational states. Initial SO{sub 2} rotational temperatures less than 3K were achieved with 0.3 mole-% of the molecule seeded in 20 atm of He. State-selective detection of the scattered products was done by LIF on the strong C(122){l_arrow}X(000) transition at 445 nm, which has been analyzed by Yamanouchi et al. Because of the selection rules and nuclear spin statistics, the k{sub a}=0 and k{sub a}=l subbands dominate the LIF spectrum. This data is currently being analyzed and the collision dynamics modelled theoretically for comparison. Cross sections for vibrational excitation in this system proved to be too small to measure.