The energetics of the OH(X 2Π, 0≤ν″≤4) product arising from the reaction of O(1D2) with the hydrocarbons CH4, C2H6, C3H8, and C(CH3)4 was fully characterized using laser-induced fluorescence (LIF). The product distribution is in sensible accord with earlier more limited LIF and infrared chemiluminescence studies, and the overall yield of OH decreases dramatically in the case of the heavier hydrocarbons as would be expected if dissociation of the collision intermediate was dominated by rupture of the relatively weak C–C bond. The energetics of the O(1D2)/CH4 reaction suggest that it proceeds via an insertion/elimination reaction, while that of O(1D2) with the heavier hydrocarbons appears to involve two parallel mechanisms. The major channel yields vibrationally and rotationally cool OH; by comparison with abstraction of hydrogen by O(3PJ) which preferentially yields vibrationally excited OH, this channel is associated with dissociation of a long-lived complex. The highly excited component of OH population arises from a prompt dissociation of a collision complex prior to statistical distribution of reaction exothermicity among its internal modes.

The thermal rate constants for collisional deactivation of electronically excited oxygen atoms, 0(2 ID 2 ), by N2• O2, N20, CO 2 , CH., and H 2 0 have been measured at 295 K. The optically metastable atoms were produced by pulsed photolysis of 0 3 at 248 nm using a KrF excimer laser and monitored by following the increase in 0(2 3P J ) concentration following quenching of 0(2 1 D 2 ) through the use of time-resolved atomic resonance spectroscopy. This method of analysis obviated difficulties associated with the evaluation of the curve-of-growth law which were encountered in previous attempts to measure the removal of 0(2 ID 2 ) using a similar technique. Rate constants reported here are in excellent agreement with those measured by observation of the weak 0(2 ID 2 }-O(2 3p J ) emission at 630 nm. In addition, it was possible to determine the extent of physical quenching in the deactivation of 0(2 ID 2 ) by H 2 0, CO 2 , CH., and N 2 0.

Partial internal energy distributions of the hydroxyl reaction products of O(1D)+H2, HD, and D2 reactions are presented. Inverted rotational distributions, preferential population of the π+ lambda doubling sublevels, and statistical population of the spin sublevels are observed. A slight preferential formation of the OD vs OH reaction products observed is measured for the reaction of O(1D)+HD. Surprisal analysis of these results indicates both dynamical and kinematic constraints on the reaction dynamics. Comparison of these results with published model calculations suggest that an insertion mechanism to form a highly energetic collision complex dominates the reaction dynamics.

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Relative values of the quantum yield of O(XD2) from the photolysis of ozone in the wavelength region 275-325 nm have been measured by observing infrared fluorescence following the reaction O(XD2) -3-CO2--•O(3pj)-3-C02((mnp), indicating multiply vibrationally excited CO 2 with m quanta in the symmetric mode v x, n in the (doubly degenerate) bend v 2, and p in the asymmetric stretch %)), using the frequency-doubled output of a narrow-band dye laser as the photolysis source. The location and shape of the falloff in O(XD2) yield near 310 nm confirms the results of previous studies made with other means of quantifying O(XD2). A "tail" in the quantum yield at longer wavelengths, not consistently observed in other experiments, is clearly evident here. The quantum yield also appears to decrease slowly at wavelengths shorter than about 290 nm. INTRODUCTION