Vibronic Structure of the Formyloxyl Radical (HCO2) via Slow Photoelectron Velocity-Map Imaging Spectroscopy and Model Hamiltonian Calculations†

We report high-resolution photoelectron spectra of HCO2- and DCO2- obtained with slow photoelectron velocity-map imaging. Well-resolved photodetachment transitions to the 2A1 and 2B2 states of the neutral radicals were observed. In addition, vibronic levels of the HCO2 and DCO2 radicals with up to 2000 cm-1 of internal energy were calculated using a quasidiabatic Hamiltonian approach and high-level ab initio calculations. Spectral simulations using the calculated levels were found to be in excellent agreement with the experimental spectra and used to assign many of its features. This study unambiguously determined that the 2A1 state is the ground state of both HCO2 and DCO2, in contrast to earlier work that indicated the 2B2 state was the ground state for DCO2. For both isotopologs, the 2B2 state is a very low-lying excited state with term energies of T0) 318 ( 8 cm-1 for HCO2 and T0) 87 ( 8 cm-1 for DCO2. The adiabatic electron affinities are determined to be EA(HCO2) ) 3.4961 ( 0.0010 eV and EA(DCO2) ) 3.5164 ( 0.0010 eV. I