Examination of the 2A′2 and 2E″ states of NO3 by ultraviolet photoelectron spectroscopy of NO−3

Abstract

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 D_3h 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.