Reaction dynamics of the nonvalence bound states of the anions

Abstract

Nonvalence bound state (NBS) is a unique anionic state where an excess electron is loosely bound to a neutral molecule in long-range potentials. Since Fermi and Teller first proposed that an electron could be bound in the dipolar field of a molecule, the physical and chemical properties of NBS in a variety of chemical systems have been investigated over recent decades. In this short review, recent notable studies aimed at thoroughly understanding the dynamics of NBS in various anionic chemical systems are elaborated. Photodetachment and photoelectron spectroscopic methods, particularly applied to cryogenically cooled anions, have been highly successful in providing detailed rovibronic structures of the NBS in many interesting chemical systems. Furthermore, real-time pump-probe photoelectron spectroscopy unraveled new dynamic aspects of anion physics and chemistry, offering deep insight into mode-specific autodetachment dynamics and the role of metastable NBS as a doorway into anionic chemical reactions. Autodetachment and/or nonvalence-to-valence (or vice versa) electron-transfer dynamics of NBS are found to be strongly mode-specific, presenting a challenge for theoretical explanations of their quantum-mechanical nature. The outlook for further exploration of NBS in various chemical or biological contexts as well as its potential exploitation in controlling chemical reaction is also provided.