Crossed-Beams Studies of the Dynamics of the H-Atom Abstraction Reaction, O(3 P) + CH4 → OH + CH3, at Hyperthermal Collision Energies

The H-atom abstraction reaction, O(3 P) + CH4 → OH + CH3, has been studied at a hyperthermal collision energy of 64 kcal mol–1 by two crossed-molecular-beams techniques. The OH products were detected with a rotatable mass spectrometer employing electron-impact ionization, and the CH3 products were detected with the combination of resonance-enhanced multiphoton ionization (REMPI) and time-sliced ion velocity-map imaging. The OH products are mainly formed through a stripping mechanism, in which the reagent O atom approaches the CH4 molecule at large impact parameters and the OH product is scattered in the forward direction: roughly the same direction as the reagent O atoms. Most of the available energy is partitioned into product translation. The dominance of the stripping mechanism is a unique feature of such H-atom abstraction reactions at hyperthermal collision energies. In the hyperthermal reaction of O(3 P) with CH4, the H-atom abstraction reaction pathway accounts for 70% of the reactive collisions, while the H-atom elimination pathway to produce OCH3 + H accounts for the other 30%.