STATE-TO-STATE RATE CONSTANTS FOR THE COLLISIONAL INTERACTION OF XE(7P), XE(6P'), AND KR(5P') ATOMS WITH HE AND AR

One-photon laser excitation of Xe(6s[3/2](2)) and Kr(5s[3/2](2)) atoms that were generated in a discharge-flow reactor was used to study the collisional relaxation of the Kr(5p'[3/2](1), [3/2](2), and [1/2](1)) , the Xe(7p[3/2](2), [3/2](1), [5/2](2), and [5/2](3)), and the Xe(6p' [3/2](1), [3/2](2), and [1/2](1)) states in He and Ar. Both cw and pul sed laser excitation techniques were utilized to obtain the total deac tivation rate constants and product formation rate constants at 300 K. Collisions with He mainly produce Xe and Kr* product states with sma ll energy defects, but the rate constants can be as large as 20X10(-10 ) cm(3) atom(-1) s(-1) which correspond to thermally averaged cross se ctions of 150 Angstrom(2). Because of the rapid collisional coupling o f populations in nearly isoenergetic levels, multicomponent exponentia l decay of the initially produced state is frequently observed. The de activation rate constants for Ar are smaller than for He, but the prod uct distributions tend to be more diverse than for He, and arguments b ased only on energy defects are riot necessarily a good guide to the f avored product state(s) from Ar collisions. The magnitude of the quenc hing cross sections for Ar is consistent with the crossing of an entra nce channel with several diabatic exit channel potentials. However, th e superlarge quenching cross sections for Xe-He to just one or two pr oduct levels require special considerations. The Kr(5p') and Xe(6p' an d 7p) rate constants with He are discussed with respect to collisional effects upon the use of cw optical pumping to convert populations in the metastable Xe(6s[3/2](2)) and Kr(5s[3/2](2)) levels to the Xe(6s'[ 1/2](0)) and Kr(5s'[1/2](0)) levels. (C) 1996 American Institute of Ph ysics.