The decay of OH was studied in a flow system of high pumping speed. Water discharges are unsuitable as sources of OH because OH is produced throughout the flow system. When produced by the very fast reaction H+N02 -+ OH+NO (1), OH was found to decay very rapidly by the steps 2 0 H + H20+0 (2), and O+OH+ Oz+H (4), with (2) rate-controlling and k2 = 2-5h0.6x 10-12 cm3 molecule-1 sec-1. This decay corresponds to a half-life of OH about 100 times shorter than has previously been reported. The decay of OH was found to be unaffected by He, Ar, N2, 0 2 , NO and H20, but an increased rate in the presence of excess H2 was ascribed to OH+H2+H20+H.No vibrationally excited OH was found and it is concluded that such species are not major reaction products. An $value calculated from the measured light absorption on the basis of reaction (1) and assuming thermally equilibrated OH is in fair agreement with recent estimates.* It must be borne in mind, of course, that the equilibrium ratio OH, v" = 1/OH, v f f = 0 is about 10-7 at 320°K and that large relative excesses of excited OH are not ruled out. Nevertheless the present results indicate that ground-state OH is the only major product of the reaction.

The infrared emission spectrum of the NO Δv=1 bands, chemiexcited in the reaction between metastable atomic nitrogen and molecular oxygen, has been studied at temperatures of 90–180 K and pressures near 5×10−6 atm. It is concluded that the observed radiation corresponds to an NO vibrational distribution created solely by the chemical reaction, unaffected by any relaxation process(es). Relative rate constants for production of NO into individual vibrational levels are found to be very nearly constant for levels v=1–7 and decrease monotonically for levels v=8–12. The average degree of excitation is about 4.5 vibrational quanta per NO molecule, and, assuming that N(2P) atoms play a negligible role, it is determined that 27% of the N(2D)+O2 exothermicity is converted to vibrational excitation of the nitric oxide product. Both the nature of the distribution and the results of a surprisal analysis suggest that those reactions which produce NO in levels higher than v=7 may also be producing O(1D).

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The line absorption method is used to determine the oscillator strength of OH, 2Σ—2Π, in a discharge-flow system. OH is made quantitatively by the rapid reaction H+NO2→OH+NO. f values for the unresolved Q1—4 doublet and P1—2 line are calculated from the measured absorption of these lines. On the well-supported assumption of Doppler-shaped emission and absorption lines and on the basis of experimental information on the translational temperature of emitting and absorbing OH molecules, a band oscillator strength, f00, of 7.1±1.1×10—4 is reported for the (0, 0) band. Application of corrections for thermochemistry and for vibration—rotation interaction to reported f values leads to improved agreement and suggests an f00 near 8×10—4.

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