Probing the Dipole-Bound State in the 9‑Phenanthrolate Anion by Photodetachment Spectroscopy, Resonant Two-Photon Photoelectron Imaging, and Resonant Photoelectron Spectroscopy

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 125; no. 14; pp. 2967 - 2976
• Main Authors: Yuan, Dao-Fu, Zhang, Yue-Rou, Qian, Chen-Hui, Liu, Yuan, Wang, Lai-Sheng
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15.04.2021
• Subjects: A: Structure, Spectroscopy, and Reactivity of Molecules and Clusters; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.1c01563

Valence-bound anions with a dipolar core can support dipole-bound states (DBSs) below the electron detachment threshold. The highly diffuse DBS observed is usually of σ symmetry with an s-like orbital. Recently, a π-type DBS was observed experimentally in the 9-anthrolate anion (9AT–) and it was shown to be stabilized due to the large anisotropic polarizability of the 9AT core. To confirm the general existence of π-DBS and its structural dependence, here we report an investigation of the 9-phenanthrolate anion (9PT–), which has a different structure and lower symmetry than 9AT–. Photodetachment spectroscopy revealed a DBS 257 cm–1 below the detachment threshold of 9PT– at 19 627 cm–1 (2.4334 eV). Resonant two-photon photoelectron imaging indeed showed a π symmetry for the DBS. Similar to that observed in 9AT–, the π-DBS in 9PT– is also stabilized by the anisotropic polarizability of the 9PT core and accessed via nonadiabatic population transfer from the initially populated σ-DBS. Photodetachment spectroscopy unveiled nine above-threshold vibrational resonances of the DBS, resulting in nine highly non-Franck–Condon resonant photoelectron spectra by tuning the detachment laser to the vibrational resonances. The combination of photodetachment spectroscopy and resonant photoelectron spectroscopy allowed frequencies for nine vibrational modes of the 9-phenathroxy radical to be measured, including the six lowest frequency bending modes.