Laser-induced fluorescence determination of the internal state distributions of OH(X2Π) produced in molecular beam reactions ofO(3P) with some cyclic hydrocarbons

Abstract

The dynamics of the hydrogen atom abstraction reactions of O(3 P) with cyclohexane, cyclohexene and 1,4-cyclohexadiene have been investigated by measuring the OH product internal state distributions by laser-induced fluorescence under crossed-molecular beam conditions. The rotational state distributions are similar for all three reactions and show that a low fraction (1–3 per cent) of the available energy goes into OH rotation. This indicates that abstraction is a direct reaction and only takes place when the O atom is collinear with the C-H bond under attack. The amount of OH vibrational excitation increases only modestly (16–22 per cent) despite a large increase in the exoergicity along the series of reactions. Comparison with the predictions of a three-body model suggests that not all of the increased exoergicity due to the stabilization energy of the hydrocarbon radical product for the reactions with the unsaturated alicyclic hydrocarbons is available for vibrational excitation of the OH and that some internal excitation of the radical takes place.