Spectroscopy and dynamics of the dipole-bound state of acetaldehyde enolate

Ultrahigh-resolution photodetachment spectroscopy of acetaldehyde enolate negative ion has revealed ∼50 narrow resonances near threshold, corresponding to excitation to a diffuse state in which the electron is weakly bound by the field of the molecular dipole. A complete analysis of rotational transitions between the ground valence state and the excited dipole-bound state has been carried out, yielding spectroscopic constants and geometries for both states. In analogy to Rydberg states, the structure of the ‘‘neutral core’’ of the dipole-bound state is like that of the neutral radical. The dependence of autodetachment lifetimes upon the rotational quantum numbers of the dipole-bound state has been measured. Bound levels of the dipole-bound anion state are readily electric-field detached. The selection rules and dynamics of autodetachment from the dipole-bound state are discussed.