A quantum chemical study of the infrared absorption intensities of the isolectronic C 3v systems NH 3, H 3O + and CH −3

Abstract

The dipole moment derivatives and the infrared absorption intensities for the isoelectronic, isostructural species NH 3, H 3O + and CH − 3, calculated by ab initio quantum methods within the double harmonic approximation, are reported. The calculations were performed at the SCF, CI and CPA″ levels of theory using basis sets of triple zeta+two polarization functions quality. For the ions H 3O + and CH − 3, in the absence of adequate experimental information, the calculations are fully ab initio, since the equilibrium geometries as well as the force constants had to be computed. The applicability of the harmonic treatment to systems with inversion potentials is discussed, especially with regard to H 3O +. The dipole moment derivatives of the three systems show interesting, regular trends in accordance with the amount of electronic charge associated with the hydrogen atoms.