Observation and ultrafast dynamics of a nonvalence correlation-bound state of an anion.

Nonvalence states of molecular anions play key roles in processes, such as electron mobility, in rare-gas liquids, radiation-induced damage to DNA, and the formation of anions in the interstellar medium. Recently, a class of nonvalence bound anion state has been predicted by theory in which correlation forces are predominantly responsible for binding the excess electron. We present a direct spectroscopic observation of this nonvalence correlation-bound state (CBS) in the para-toluquinone trimer cluster anion. Time-resolved photoelectron velocity map imaging shows that photodetachment of the CBS produces a narrow and highly anisotropic photoelectron distribution, consistent with detachment from an s-like orbital. The CBS is bound by ~50 meV and decays by vibration-mediated autodetachment with a lifetime of 700 ± 100 fs. These states are likely to be common in large and/or polarizable anions and clusters and may act as doorway states in electron attachment processes.