Formation of OH(v=0,1) by the reaction of fast H with O3

A two-laser, pump-probe experiment has been used to determine the rotational level population distribution of OH(upsilon=0,1) resulting from the reaction of fast (2.3 eV) hydrogen atoms with ozone. A trace amount of H2S in slowly flowing O-3 was photolyzed at 193 nm, and the resultant OH was detected using laser-induced fluorescence (LIF). The pump-probe delay time was adjusted in order to verify negligible relaxation of the nascent OH product. Initially, side reactions such as O(D-1) +H2S --> OH + HS were found to contribute to the OH signals; they were subsequently eliminated by adjusting the reactant concentrations and flow velocity. The resultant OH LIF spectra were corrected for several factors using either known or measured experimental quantities, including OH(A) collisional quenching, baseline drift, and partial saturation of the OH(A-X) absorption lines. Near-gas kinetic rate constants for OH(A,upsilon'=0,N'less than or equal to 25) collisional quenching by O-3 were derived. The corrected spectra were fit using a nonlinear least-squares routine to infer individual N-level populations for OH(upsilon=0,1). The spin-orbit (F-1 and F-2) and lambda-doublet (IT(A') and n(A ")) populations were inferred in a separate least-squares fit by comparing the intensities of different OH(A-X) rotational branches. The OH upsilon=1: upsilon=0 population ratio is equal to 0.37 +/- 0.04. For both upsilon levels the rotational level populations increase gradually with N, with the population in N = 20 about 5 times that in N = 1. The F-1:F-2 and Pi(A'):Pi(A ") population ratios are equal to 1.03 +/- 0.28 and 1.34 +/- 0.20, respectively.