Channel branching ratios in CHCN photodetachment: Rotational structure and vibrational energy redistribution in autodetachment.

We report photoelectron spectra of CHCN, recorded at photon energies between 13 460 and 15 384 cm, which show rapid intensity variations in particular detachment channels. The branching ratios for various spectral features reveal rotational structure associated with autodetachment from an intermediate anion state. Calculations using equation-of-motion coupled-cluster method with single and double excitations reveal the presence of two dipole-bound excited anion states (a singlet and a triplet).