Knowledge Bank

Interest in the photodissociation mechanism of alkyl nitrates (RONO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$, where R = CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$, C$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}$, etc.) stems from recent experimental measurements in the troposphere indicating that they are an important component of ``missing NO''. In this study, the photodissociation dynamics of methyl nitrate, CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ONO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$, at 193 nm have been investigated by examining the products from the primary channel, namely, CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$O and NO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$. Laser-induced fluorescence (LIF) spectroscopy was employed to probe the nascent internal energy distribution of the CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$O radical, a small fraction of which was found to be produced with one quantum of C$\backslash relbar$O stretch excitation. The stretch-excited methoxy was observed to be formed with a significantly greater degree of rotational excitation than the vibrational ground state. Furthermore, dispersed fluorescence measurements reveal that the NO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ fragment is produced electronically excited with internal energies out to the NO + O dissociation limit, indicating that the initial excitation is strongly localized on the NO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ moiety. Comparisons will be drawn with the analogous photodissociation of nitric acid, HONO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$.