Threshold photodetachment of HOCO$^-$: a theoretical study

The HOCO radical is an important intermediate in combustion. Information about its electronic structure has been obtained from studies of the photodetachment of HOCO$^-$. We present the results of a theoretical study of HOCO$^-$ photodetachment, with a view toward understanding the origin of two peaks observed in the photoelectron kinetic energy spectrum very close to threshold. Fixed-nuclei variational electron-HOCO scattering calculations are used to compute photodetachment cross sections and laboratory-frame photoelectron angular distributions. We show that the observed peaks cannot, as previously assumed, be narrow shape resonances and argue that they can be attributed to vibrational Feshbach resonances of dipole-bound trans-HOCO$^-$.