Photodetachment of Isolated Bicarbonate Anion: Electron Binding Energy of HCO3(.).

We report the first direct photodetachment photoelectron spectroscopy of HCO3(-) in the gas phase under low-temperature conditions. The observed photoelectron spectra are complicated due to excitations of manifolds in both vibrational and electronic states. A long and single vibrational progression with a frequency of 530 ± 20 cm(-1) is partially resolved in the threshold of the T = 20 K, 266 nm spectrum. The adiabatic electron detachment energy (ADE) of HCO3(-), or, in other words, the electron affinity (EA) of neutral HCO3, is experimentally determined from the (0,0) transition to be 3.680 ± 0.015 eV. The computed values of the Franck-Condon integral and intensity are favorable for observing the (0,0) transition. High-level ab initio calculations at the CCSD(T) level of theory produce an estimated anharmonic frequency of 546 cm(-1) for HCO3 and a value of 3.79 eV for the (0,0) transition, both in good agreement with the experimentally determined values.