Observation of Core-Excited Dipole-Bound States

• Published in: The journal of physical chemistry letters Vol. 13; no. 9
• Main Authors: Zhang, Yue-Rou, Yuan, Dao-Fu, Wang, Lai-Sheng
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 28.02.2022
• Subjects: Anions; Binding energy; Excited states; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Molecules; Pyrazolyl
• ISSN: 1948-7185; 1948-7185

Polar molecules can bind an electron in a diffuse orbital due to the charge-dipole interaction. Electronic excited states of polar molecules can also bind an electron to form core-excited dipole-bound states (DBSs), analogous to core-excited Rydberg states. However, core-excited DBSs have not been observed because of the complicated electronic structure of molecular systems. Here we report the observation of a core-excited DBS in the pyrazolide anion as a result of the favorable electronic structure of the neutral pyrazolyl core, which has a low-lying excited state ($\tilde{A}$ 2B1) only 266 cm-1 above its ground state ($\tilde{X}$ 2A2). The binding energy of the DBS associated with the ground state is measured to be 221 cm-1, while that of the core-excited DBS is 276 cm-1, which is still a bound state relative to the detachment threshold. Furthermore, vibrational Feshbach resonances are observed for both DBSs and their autodetachment behaviors are studied by resonant photoelectron imaging.