UC San Diego
Investigation of Reactive Oxides and Radical Dynamics by Photoelectron-Photofragment Coincidence Spectroscopy
- Author(s): Lunny, Katharine
- Advisor(s): Continetti, Robert E
- et al.
Carbon, hydrogen, oxygen, and nitrogen are the most common elements necessary for life and in combination create a multitude of molecules. These include highly reactive species with complicated electronic structures, such as oxygenated hydrocarbon radicals and nitrogen oxides. These short-lived species can be important in atmospheric and combustion processes, but difficult to characterize due to their transient nature. Photoelectron-photofragment coincidence spectroscopy is a technique designed to study short-lived species thought photodetachment of the corresponding stable anion and measure the energy partitioning within the neutral species.
The oxyallyl anion was photodetached to the nearly degenerate states, 3B2 and 1A1 as well the 3B1 excited state, which were correlated to predominately stable C3H4O neutral. The photoelectron spectrum of the oxyallyl diradical and the acetone enolate radical, C3H5O, are the correct assignment for the C2O2 and HC2O2 photoelectron spectra reported in the literature. The oxyallyl diradical was observed to have a minor dissociation channel, at both Ehν = 3.20 eV and 1.60 eV. At Ehν = 3.20 eV, photodetachment to the 1A1 state is accessible, and results in dissociation to CO + C2H4. Dissociation was also observed from the triplet states, occurring after intersystem crossing. This system is further complicated by the observation of dipole bound states. The 1A1 state has a zwitterionic character resulting in observation of photodetachment ~0.3 eV below threshold. A stable neutral was the result of delayed photoemission during cyclization, as well as dissociative photodetachment resulting from a two photon process were observed.
The complicated electronic structure of nitrogen oxides, N2O2 and NO3 exhibit photodissociation pathways due the several neutral dissociation channels accessible at Ehν = 3.20 eV. For N2O2, photodissociation resulted in vibrationally excited NO anions which undergoes autodetachment, as well as photodissociation of NOˉ (ν=0). Photodissociation was also observed to result in N2O + Oˉ which undergoes sequential photodetachment. The peroxynitrite anion, a high energy isomer of the nitrate anion, was also observed to produce similar photodissociation pathways. Vibrationally excited NOˉ followed by autodetachment was observed, as well as the observation of sequential photodetachment of O2ˉ via a two-photon process.