Formation of OH(v=0,1) by the reaction of fast H with O-3

A two-laser, pump-probe experiment has been used to determine the rotationa l level population distribution of OH(upsilon=0,1) resulting from the react ion of fast (2.3 eV) hydrogen atoms with ozone. A trace amount of H2S in sl owly flowing O-3 was photolyzed at 193 nm, and the resultant OH was detecte d using laser-induced fluorescence (LIF). The pump-probe delay time was adj usted in order to verify negligible relaxation of the nascent OH product. I nitially, side reactions such as O(D-1) +H2S --> OH + HS were found to cont ribute to the OH signals; they were subsequently eliminated by adjusting th e reactant concentrations and flow velocity. The resultant OH LIF spectra w ere corrected for several factors using either known or measured experiment al quantities, including OH(A) collisional quenching, baseline drift, and p artial saturation of the OH(A-X) absorption lines. Near-gas kinetic rate co nstants for OH(A,upsilon'=0,N'less than or equal to 25) collisional quenchi ng by O-3 were derived. The corrected spectra were fit using a nonlinear le ast-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 ")) p opulations were inferred in a separate least-squares fit by comparing the i ntensities of different OH(A-X) rotational branches. The OH upsilon=1: upsi lon=0 population ratio is equal to 0.37 +/- 0.04. For both upsilon levels t he rotational level populations increase gradually with N, with the populat ion in N = 20 about 5 times that in N = 1. The F-1:F-2 and Pi(A'):Pi(A ") p opulation ratios are equal to 1.03 +/- 0.28 and 1.34 +/- 0.20, respectively .