Force constants of CF 4, SiF 4, BF 3, CH 4, SiH 4, NH 3, and PH 3

Abstract

The general force constants are calculated from the observed frequencies, the Coriolis coupling constants and the available isotope shifts of frequencies for CF 4 and SiF 4. The off-diagonal force constants obtained are explained by the Lennard-Jones type nonbonded fluorine-fluorine interaction. The vibration frequencies, their isotope shifts and the Coriolis constants of BF 3 are also explained by the same interaction. Force constants of CCl 4, CBr 4, CI 4, SiCl 4, SiBr 4, SiI 4, BCl 3, BBr 3, and BI 3 are obtained by similar methods. For CH 4, SiH 4, NH 3, and PH 3 a set of the elements of F-matrices has been obtained which gives the vibrational frequencies of these molecules, those of CH 3D, CH 2D 2, CHD 3, CD 4, SiD 4, ND 3, and PD 3 and the Coriolis coupling constants in agreement with the observed ones. The magnitudes of the obtained off-diagonal elements are discussed. They are in agreement with those calculated from Buckingham's nonempirical formula for the hydrogen-hydrogen nonbonded interaction.