I(P-2(1 2))+O-2 - STUDIES OF LOW-TEMPERATURE ELECTRONIC-ENERGY TRANSFER AND NUCLEAR SPIN-STATE CHANGING COLLISIONS/

Energy transfer between I(P-2(1/2)) and O-2(X) was examined in a Laval nozzle expansion at temperatures near 150 K. The rate constant for el ectronic energy transfer was found to be k(b)(150) = (7.0 +/- 0.7) X 1 0(-12) cm(3) s(-1), which was a factor of 1.5 greater than a previous low-temperature determination [T. Van Marter, M. C. Heaven, and D. Plu mmer, Chem. Phys. Lett. 260, 201 (1996)]. Laser induced fluorescence ( LIF) detection of I(P-2(1/2)) via the 5p(4)6s(P-2(3/2)) -5p(5)(P-2(1/2 )) transition was demonstrated. The 5p(5)(P-2(1/2))F = 2 and F = 3 hyp erfine sublevels were resolved in the LIF spectrum, permitting observa tion of the kinetics associated with transfer between F = 2 and 3. I(P -2(1/2)) was generated by 498 nm photolysis of I-2. The nascent popula tion distribution of the hyperfine levels was found to be nonstatistic al, with N(F = 2)/N(F = 3) = 1.3 +/- 0.1. Collisions with O-2(X) cause d F = 3 double left right arrow F = 2 transfer. Analysis of the F = 2 and 3 decay kinetics yielded hyperfine transfer rate constants of k(2 double right arrow 3) = (2.6 +/- 0.3) x 10(-11) and k(3 double right a rrow 2) = (1.9 +/- 0.2) x 10(-11) cm(3) s(-1) (T = 150 K). Both the el ectronic energy transfer and the hyperfine transfer rate constants are of relevance to supersonic oxygen iodine lasers, as these devices ope rate on the (P1/2F)-P-2 = 3 double right arrow (P3/2F)-P-2 = 4 transit ion, in the presence of a relatively high pressure of O-2. (C) 1998 Am erican Institute of Physics. [S0021-9606(98)01445-7].