Influence of the collision energy on the O({sup 1}D) + RH {r{underscore}arrow} OH(X{sup 2}II) + R (RH = CH{sub 4}, C{sub 2}H{sub 6}, C{sub 3}H{sub 8}) reaction dynamics: A laser-induced fluorescence and quasiclassical trajectory study

The influence of the collision energy (E{sub T}) on the O({sup 1}D) + RH {r{underscore}arrow} OH(X{sup 2}II) + R (RH = CH{sub 4}, C{sub 2}H{sub 6}, and C{sub 3}H{sub 8}) reaction dynamics has been studied, using the N{sub 2}O photodissociation at 193 nm as O({sup 1}D) precursor ({l{underscore}angle}E{sub T}{r{underscore}angle} = 0.403 eV) and probing the OH {upsilon}{double{underscore}prime} = 0 and 1 levels by LIF. A triatomic QCT study of the reaction with CH{sub 4} on a fully ab initio based analytical PES has also been performed, and a quite good agreement with the experimental OH rovibrational distributions has been obtained. The authors experimental results are similar to those obtained when the O{sub 3} photodissociation is used to produce O({sup 1}D) ({l{underscore}angle}E{sub T}{r{underscore}angle} = 0.212 eV), as expected on the basis of the available energy in products and also from the QCT calculations. The P({upsilon}{double{underscore}prime} = 0)/P({upsilon}{double{underscore}prime} = 1) populations ratio values reported for C{sub 2}H{sub 6} and C{sub 3}H{sub 8} in a very recent work (Wada and Obi, J.Phys.Chem.A 1998, 102, 3481), where the N{sub 2}O was also used to generate O({sup 1}D), are probably largely underestimated. The rotational distributions obtained are similar to those obtained in other experiments, and a quite good agreement has been obtained for the spin-orbit and {Lambda}-doublet populations. The reaction takes place near exclusively through the insertion of the O({sup 1}D) atom into a C-H bond below 0.6 eV, and the mechanism may be direct or nondirect (mainly through short-lived (CH{sub 3})OH collision complexes) with about the same probability. The OH vibrational distribution arising from the direct mechanism is inverted, while the nondirect one leads to a noninverted distribution. A higher E{sub T}, the abstraction mechanism also contributes appreciably to reactivity.