A theoretical investigation of the vibrational states of HCO2- and its isotopomers

Abstract

Making use of the coupled cluster variant CCSD(T) and the aug-cc-pVQZ basis set a six-dimensional (6D) potential energy surface has been calculated for HCO2-, a fundamental organic anion. Therefrom, a variety of vibrational term energies and wavefunctions has been obtained by means of the discrete variable representation in an approach termed DVR(6). Calculated wavenumbers of the fundamentals of HCO2- and DCO2- agree with recent experimental values from neon matrix isolation IR spectroscopy within 15 cm(-1). The out-of-plane bending vibrations nu(4) are predicted at 1030 and 894 cm(-1). Moderately strong Fermi resonance interaction is calculated between vibrational states nu(1) and 2nu(4) of DCO2-. Excellent agreement with experiment (differences less than 0.7 cm(-1)) is observed for the C-13 and O-18 isotopic shifts. Accurate ground-state rotational constants are predicted for eight different isotopomers of the formate ion and the dissociation process HCO2- --> H- + CO2 is investigated in some detail, with the dissociation energy D-0 predicted to be 216 kJ mol(-1).