Theory of Nuclear Quadrupole Interactions in Solid Fluoromethanes with Implanted 19F* Nuclei. Coupling of HF* and Host Molecule

Abstract

Abstract The Quadrupole Coupling Constant e2qQ and Asymmetry Parameter η of fluorine for fluorine-substitute methane compounds are calculated using the Hartree-Fock Roothaan procedure. Our results are compared with experimental data from measurements by the Time Differential Perturbed Angular Distribution (TDPAD) technique using excited 19F* (spin 5/2) nuclei. The theoretical e2qQ’s for the 19F* nuclei in the fluoromethanes are in good agreement with experimental results. For CH2F2 and CHClF2 molecules, where finite η are expected from symmetry considerations, our results for η are small, 0.12 and 0.05 respectively, in agreement with experimental observation. Besides the 19F* coupling constants associated with the C-F bonds in fluoromethanes, additional interesting NQI parameters, close to those in solid hydrogen fluoride, are observed in the TDPAD measurements. It is demonstrated through investigations of the total energies and electric field gradients that these additional NQI parameters for the fluoromethanes can be explained by a HF* molecule hydrogen-bonded through the hydrogen to a fluorine atom in the host molecular systems. This complexing of an ionic molecule to the host molecules in organic solids containing strongly electronegative atoms is expected to be a general feature in both implantation and conventional techniques.