High-Resolution Photoelectron Spectroscopy of NO3 – Vibrationally Excited Along Its ν3 Mode

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 129; no. 6; pp. 1634 - 1647
• Main Authors: Lau, Jascha A., DeWitt, Martin, Franke, Peter R., Stanton, John F., Neumark, Daniel M.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 13.02.2025
• Subjects: A: Structure, Spectroscopy, and Reactivity of Molecules and Clusters; Anions; Infrared light; Lasers; Phase transitions; Photodetachment
• ISSN: 1089-5639; 1520-5215; 1520-5215
• DOI: 10.1021/acs.jpca.4c07682

The nitrate (NO3) radical has long been the subject of both experimental and theoretical studies due to its complex electronic structure resulting from vibronic interactions between its X̃ 2 A 2 ′ and B̃ 2 E ′ states. In particular, the definite assignment of the fundamental of its degenerate stretching vibration (ν3) is still under debate. Here, we report high-resolution photoelectron spectra of vibrationally pre-excited NO3 – using the recently developed IR-cryo-SEVI technique. The anions are excited through infrared (IR) excitation near 1350 cm–1, accessing the ν3 and 2ν3(e′) vibrational levels with band centers at 1350.5 and ∼2700 cm–1, respectively. The IR-cryo-SEVI spectrum for 2ν3 pre-excitation shows clear evidence for an intense 32 1 transition. From the position of this feature (30031 cm–1), the electron affinity of NO3 also determined in this work (31680 cm–1), and the IR excitation energy, we obtain a fundamental frequency of 1051 cm–1 for the ν3 fundamental of the NO3 radical. This assignment and other features in the IR-cryo-SEVI spectra are supported by spectral simulations based on a vibronic Köppel–Domcke–Cederbaum Hamiltonian. The simulations also show that nearly all features in the IR-cryo-SEVI spectra arise because of pseudo-Jahn–Teller coupling between the X̃ and B̃ states of NO3. The results and analysis presented here settle a long-standing controversy regarding the ν3 frequency of NO3.