MCSCF/CI ground state potential energy surface, dipole moment function, and gas phase vibrational frequencies for the nitrogen dioxide positive ion

Abstract

The ground state potential energy surface for the nitrogen dioxide positive ion, NO+2X 1Σ+g(Σ+,A1,A′), has been scanned with a correlated wave function to obtain directly, for the first time, the gas phase equilibrium geometry, force constants, vibrational frequencies, and dipole moment function. The wave function for this scan was constructed from a double-zeta plus polarization one-electron basis with a 12 configuration MCSCF determination of the orbital basis for a full valence 1Σ+g configuration interaction expansion. The calculated equilibrium bond length is 1.12 Å. The vibrational frequencies are computed to be ν1=1514, ν2=679, and ν3=2614 cm−1 The present ab initio results differ significantly from crystalline spectroscopic studies and are, thus, the best values available for the gas phase vibrational frequencies. The dipole moment function is nonzero at the Σ+, A1, and A′ geometries included in the potential surface scan, and is obtained here to provide for the future a priori calculation of the infrared band intensities.