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.