The anharmonic potential function of methylene fluoride. SCF ab initio computations of the cubic force field and analysis of vibration-rotation interaction constants

The harmonic and the cubic force fields of CH2F2 have been evaluated ab initio from the SCF energy expression by analytic derivative methods. The computed cubic force constants were used as starting values in a least squares analysis of the experimental vibration-rotation constants of CH2F2 and CD2F2. A simple scaling procedure of the ab initio cubic force constants provides a complete cubic force field for the molecule and the best fit with the experimental data.