Photodissociation of CH3OCl to CH3O + Cl at 248 nm

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 108; no. 10; pp. 1650 - 1656
• Main Authors: Krisch, M. J, McCunn, L. R, Takematsu, K, Butler, L. J, Blase, F. R, Shu, J
• Format: Journal Article
• Language: English
• Published: American Chemical Society 11-03-2004
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp0372082

This study examines the 248 nm photodissociation of methyl hypochlorite (CH3OCl), a molecule that serves as an atmospheric chlorine reservoir. The data show that the primary photodissociation channel is cleavage of the O−Cl bond to produce Cl atoms and CH3O radicals, a result consistent with the direct dissociation mechanism found by other computational and experimental studies of alkyl hypohalites. Photofragment translational spectroscopy with a crossed laser-molecular beam apparatus, coupled with tunable VUV photoionization detection, identified the momentum-matched products at m/e = 35 (Cl+ from Cl atoms) and m/e = 29 (the CHO+ daughter ion of CH3O). Products were formed with a narrow range of recoil kinetic energies, peaking at 48 kcal/mol in the center-of-mass reference frame, with a full-width half-maximum of 4 ± 2 kcal/mol. This kinetic energy distribution shows that the CH3O products are formed with a very narrow range of internal energies, and a simple model shows that to conserve angular momentum this internal energy, near 20 kcal/mol, is partitioned primarily to rotational energy. Thus CH3OCl could serve as a photolytic precursor of CH3O radicals with high and well-defined rotational and translational energies.