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The photoelectron spectrum of the NO−3 anion has been obtained at 266 and at 213 nm. The 266 nm spectrum probes the 2A′2 ground state of NO3. The 213 nm spectrum represents the first observation of the 2E″ lowest-lying excited state of NO3. The 2A2 band shows vibrational progressions in the ν1 symmetric stretch and the ν4 degenerate in-plane bend of NO3. Our analysis of this band indicates that the NO3 ground state has a D3h equilibrium geometry and is vibronically coupled to the 2E′ second excited state via the ν4 mode. We also obtain the electron affinity of NO3, 3.937±0.014 eV, and the heat of formation of NO3 at 298 K, 0.777±0.027 eV (17.9±0.6 kcal/mol). The 2E″ state of NO3 lies 0.868±0.014 eV above the ground state. The 2E″ band shows complex and extensive vibrational structure. Several possible assignments of this structure are discussed.
Weaver et al. (Fri,) studied this question.