An improved anharmonic force field of CHClF2 Original Research Article

The potential energy function for CHClF2 has been investigated theoretically using standard methods in quantum chemistry. Electronic correlation effects were explicity taken into account and the harmonic components of the potential have been evaluated by Møller-Plesset theory to second order (MP2). To reduce the computational effort the cubic and quartic force fields were evaluated by Hartree-Fock theory (HF) in the Cartesian representation and then converted to the MP2 normal coordinates. A detailed comparison with experiment proved that this procedure is effective and gave a good description of vibrational and rotational energy levels and of the related spectroscopic parameters. We have finally shifted the origin of our force field and scaled the potential to reproduce to very high accuracy the experimental values of ground state rotational constants, fundamental, overtones, centrifugal distortion, vibration-rotation constants. A numerical procedure for the final fitting is described. The scallig of the force field has been performed in the curvilinear internal coordinate representation using spectroscopic data of several molecular isotopes.