Molecular structure, vibrational frequencies, and energetics of the HCO, HOCO, and HCO2 anions

The structures and vibrational spectra for HCO-, HOCO-, and HCO2- have been calculated at high levels of electronic structure theory. The changes in the structure of HCO- relative to neutral HCO are consistent with the predictions based on photodetachment experiments. Of the two isomers, HCO2- and HOCO-, the HCO2- anion is predicted to be the more stable. For HOCO-, the cis conformer is of lower energy as compared to the trans. Conversely, for neutral HOCO, the trans conformer is lower in energy. The electron affinity of HCO is predicted to be 0.308 eV in excellent agreement with the experimental value of 0.313 eV. The electron affinity of HOCO is predicted to be 1.42 eV and there is no known experimental measurement. The electron affinity of HCO2((2)A(1)) is predicted to be 3.51 eV as compared to the experimental value of 3.498 +/- 0.015 eV. The (2)A(1) state of HCO2 is predicted to be the ground state on the basis of theoretical calculations, which are in agreement with the experimental assignment determined from the photoelectron spectra.