High-Resolution Photoelectron Spectroscopy of Cryogenically Cooled NO ₃

Abstract

High-resolution anion photoelectron spectra of cryogenically cooled NO₃̅ anions obtained using slow photoelectron velocity-map imaging are presented and provide new insight into the vibronic structure of the corresponding neutral radical. A combination of improved spectral resolution, measurement of energy-dependent intensity effects, temperature control, and comparison to theory allows for full assignment of the vibronic features observed in this spectrum. We obtain a refined electron affinity of 3.9289(14) eV for NO₃. Further, the appearance of Franck-Condon forbidden transitions from vibrationally cold anions to neutral states with excitation along the NO₃ ν₄ mode confirms that these features arise from vibronic coupling with the B̃²E' excited state of NO₃ and are not hot bands, as has been suggested. Together, the suite of experimental and simulated results provides clear evidence that the ν₃ fundamental of NO₃ resides near 1050 cm^-1, addressing a long-standing controversy surrounding this vibrational assignment.