15min:

ERIKA L. DERRO, CRAIG MURRAY, MARSHA I. LESTER, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104; AND MARK D. MARSHALL, Department of Chemistry, Amherst College, Amherst, MA 01002.

The methoxy (CH₃O) radical has attracted a great deal of attention in the literature due to its unique spectroscopy, as well as its importance as a reactive intermediate in combustion and atmospheric chemistry. In this study, we employ CH₃O as a dynamical probe of the photodissociation dynamics of methyl nitrate, CH₃ONO₂, at 193 nm. Rotationally-resolved spectra of the CH₃O photoproduct were recorded in the A²A₁\relbar X²E system under both nascent and jet-cooled conditions using laser-induced fluorescence (LIF) spectroscopy. CH₃O A²A₁\relbar X²E transitions could be simulated effectively using known spectroscopic constants at the lowest temperatures achieved under jet-cooled conditions. Spectra recorded at warmer temperatures are being used to refine reported spectroscopic constants. Under nascent conditions, transitions were observed from the vibrationless level of CH₃O (X²E) as well as with C\relbarO stretch vibrational excitation, and the vibrational branching ratio is determined. The rotational excitation of these vibrational bands was fit to a Boltzmann distribution to extract nascent rotational temperatures. The experimental data indicate that the CH₃O fragment is produced with minimal internal energy (1% of the available energy) following photodissociation of CH₃ONO₂ at 193 nm.