A THEORETICAL INVESTIGATION OF H2C4H+ AND THE PROTON AFFINITY OF HC4H

A six-dimensional anharmonic potential and electric-dipole-moment surface have been calculated for H2C4H+, an ion of interest to combustion processes and astrochemistry, using CEPA-1 and a basis set of 102 contracted Gaussian-type orbitals. Vibrational frequencies and IR intensities are calculated variationally from an approximate vibrational Hamiltonian. The ν3 band of H2C4H+, with predicted origin of 2010±10 cm-1, has a large IR intensity and should be suitable for a forthcoming diode-laser investigation. The equilibrium dipole moment is as small as -0.085 D and H2C4H+ is thus no good candidate for radioastronomy. The proton affinity of HC4H is calculated to be 741 kJ mol-1, in reasonable agreement with an experimental value of 753±4 kJ mol-1. © 1990.