Influence of intermolecular bonding on nuclear quadrupole interaction tensors in solid halogens

The role of intermolecular bonding in solid halogens is studied using the self-consistent charge extended Hückel procedure. It was found that the hybridization of s and d orbitals to p orbitals of the halogen plays a very important role in the intermolecular bonding. In particular it was found that the hybridization is stronger with (n+1) s and nd orbitals where n=3,4,5 for chlorine, bromine, and iodine than for ns orbitals. Using the ns, (n+1) s, np, and nd orbitals for the halogen atom and a number of its nearest neighbors, the wavefunctions of the interacting molecules have been calculated, and using these calculated wavefunctions, the field-gradient tensors have been evaluated for all three systems. The asymmetry parameters are found to be 0.06, 0.18, 0.23 for chlorine, bromine, and iodine, respectively. The quadrupole coupling constants were found to be −109.10, −779.31, and −1923.97 MHz for chlorine, bromine, and iodine. Relativistic corrections have been incorporated in the evaluation of the field gradient. The nature of the agreement between experiment and theory for both the quadrupole coupling constants and asymmetry parameters is discussed in detail.