Photodissociation of Methyl Nitrate in a Molecular Beam

Article abstract of DOI:10.1021/j100144a002

The photodissociation of methyl nitrate, CH3ONO2, has been investigated by photofragment translational spectroscopy.At the photolysis wavelength of 193 nm the predominant primary decay (ca. 70percent) involves the fission of the weak CH3O-NO2 bond (D¹₀ ca. 41 kcal/mol) to yield CH3O + NO2 fragment pairs which show a bimodal translational energy distribution.The component consisting of the fast fragment pairs has an average translational energy (E_T) = 41 kcal/mol and a recoil anistropy β = 0.9, while the slow component is characterized by (E_T) = 19 kcal/mol and β = 0.A significant portion of the NO2 fragments of the slow component is subject to a unimolecular decay to NO + O(³P).An additional primary decay route leads to the formational of methyl nitrite, CH3ONO, and atomic oxygen O(¹D) with (E_T) = 6 kcal/mol and β = 1.2.This competing reaction requires fission of the strong N-O bond (D¹¹₀ ca. 118 kcal/mol) and its occurrence indicates an initial localization of the photoexcitation on the NO2 moiety in the parent molecule.At higher laser fluence secondary photodissociation of the primary fragments CH3ONO was observed.Photolysis at 248 nm is shown to produce CH3O + NO2 fragment pairs exclusively, with (E_T) = 17 kcal/mol.