Vibrational properties of polyatomic molecules by quantum-chemical methods

Abstract

A contracted gaussian basis set in double-zeta form (plus polarization functions) has been used to calculate the vibrational characteristics of CH3F by means of an ab-initio SCF finite-difference method. The diagonal force constants, with an error of about 10 per cent, are an upper limit to experiment. The off-diagonal interaction constants give a correct picture of the molecular force field, unlike the Hybrid Orbital Force Field model. With the derivatives of a dipole moment corresponding to a good theoretical evaluation (about 2D), it is possible to discuss the problem of signs in infra-red intensity analysis.