Chemical dynamics of the reactions of O(1D2) with saturated hydrocarbons

Abstract

Nascent OH internal state distributions produced in the reactions of O(1D2) with saturated hydrocarbons have been measured by combining laser photolysis initiation of the reactions with laser induced fluorescence detection of the OH product. The OH rotational distributions are bimodal. One component corresponds to a broad distribution of high rotational states characterized by a linear surprisal. The other corresponds to population of only the lowest few OH rotational states. These are interpreted as due to insertion and abstraction, respectively. The insertion component dominates for small hydrocarbons (CH4, C2H6), while the abstraction component is the dominant mechanism for production of OH from larger hydrocarbons [C3H8, C(CH3)4]. The large vibrational and rotational surprisals for the insertion component imply that OH is produced by a prompt, non-RRKM decay of the alcohol collision complex. For the smaller hydrocarbons, insertion preferentially populates the lower Λ-doublet component of OH. Since the rotational state distribution for the abstraction component is quite similar to that observed in the reactions of O(3P) with saturated hydrocarbons, it is suggested that abstraction results from the 1A′ to 3A″ surface crossing in the entrance channel of the insertion path.