A THEORETICAL INVESTIGATION OF THE PROPARGYL RADICAL AND ITS CATION

Large-scale ab initio calculations have been carried out for the propa rgyl radical (H2C3H) and its cation. Both have rather similar planar e quilibrium geometries so that the first band of the photoelectron spec trum is expected to show little structure. Our calculations confirm th e assignment of matrix absorptions at 686.5 and 483.5 cm(-1) to the CH 2 wagging and out-of-plane CCH bending vibrations, respectively. A str ong band at 621 cm(-1) is predicted for the in-plane CCH bending vibra tion. The equilibrium dipole moment of H2C3H is calculated to be small ; we recommend \mu(e)\ = 0.14 D. The calculated adiabatic ionization p otential of 8.65 eV is in excellent agreement with the recent experime ntal value of 8.67+/-0.02 eV.