Feshbach states of the propadienylidene anion H2CCC−

Abstract

The absorption spectra of the propadienylidene anions, H₂CCC⁻ and D₂CCC⁻, in the visible and near-UV range were recorded by photodetachment spectroscopy. The lowest excited state is the well characterized dipole bound òA₁ showing bound levels and vibrational Feshbach resonances. The higher lying electronic states are Feshbach resonances 0.5–2 eV above the electron detachment threshold and are assigned to the ²A″, ²A₁ and ²B₁←²B₁ electronic transitions by means of ab initio calculations. The autodetachment rate increases with energy. A comparison of the laboratory data with diffuse interstellar bands shows that not only the four strong transitions of the à ²A₁←²B₁ system but also several of the Feshbach resonances lie close to astronomical absorptions.