Photodetachment spectrum of 1-C3H1-:: The role of dipole bound states for electron attachment in interstellar clouds

The electronic spectrum of the linear propadienylidene anion has been recorded at 50 K by 1-C3H2- resonance-enhanced two-photon detachment spectroscopy. This resembles the absorption spectrum to the dipole bound state involving bound-bound and bound-free transitions. The wavelength of the K = 1 <-- 0 component for the origin and three vibrational bands match the weak and narrow diffuse interstellar bands. To explain the abundance of this carrier in interstellar clouds, the ratio of anions to neutrals is estimated for small polar molecules with high electron affinities using chemical considerations. An appreciable amount of anions can result in diffuse clouds because the electron attachment to polar molecules is enhanced via dipole bound states.