Ab initio anharmonic force field, molecular parameters, equilibrium structure and enthalpy of formation of fluoroform

The quadratic, cubic and semi-diagonal quartic force field of fluoroform has been calculated at the CCSD(T) level of theory employing a basis set of at least polarized valence triple zeta quality. This force field was used to predict the spectroscopic constants, including the parameters specific to the doubly degenerate vibrational states. The calculated values are not always in good agreement with the experimental data. A careful examination of the calculations and of the experimental spectra indicates that the analysis of some spectra is still not satisfactory because important interactions have been neglected. The equilibrium structure was derived from the experimental ground-state rotational constants and the ab initio rovibrational interaction parameters. This semi-experimental structure is in excellent agreement with the ab initio equilibrium geometry. Finally, an accurate value of the enthalpy of formation of CHF3 was calculated.