Chemical applications of molecular quantum theory

Molecular systems of chemical interest are investigated with the aid of molecular quantum theory. The self-consistent field (SCF) method is used to predict the molecular structures of ClF/sub 2/, ClF/sub 4/ and Cl/sub 3/ radicals, and the ions ClF/sub 2//sup +/, ClF/sub 2//sup -/, ClF/sub 4//sup +/ and ClF/sub 4//sup -/. The ClF/sub 2/ and Cl/sub 3/ radicals are predicted to be bent with bond angles of 145.2/sup 0/ and 158.6/sup 0/, respectively, while the ions ClF/sub 2//sup +/ and ClF/sub 2//sup -/ are predicted to be bent with a bond angle of 97.4/sup 0/ and linear, respectively. The geometry predictions for the ClF/sub 4/ radical and the ClF/sub 4//sup +/ ion are found to be notably basis set dependent. The ClF/sub 4//sup -/ ion is predicted to be square-planar. Multi-configuration self-consistent field (MCSCF) calculations have yielded the dipole moment function for the /sup 1/sigma/sup +/ state of HI, which qualitatively confirms the experimental finding that the dipole derivative at R/sub e/ is negative. The /sup 2/sigma/sup +/ F + H/sub 2/ potential energy surface is studied extensively with the configuration interaction (CI) method. The most complete calculations yield an activation energy of 2.74 kcal/mole and an exothermicity of 30.0 kcal/mole. The production of a potential energy surface of ''chemical accuracy'' for this system is found to be more difficult than previously believed. The simplest hydrophobic model, the water-methane system, is studied with the SCF method in order to determine the nature and magnitude of the interaction. The most favorable geometric arrangement corresponds to an attraction of 0.5 kcal/mole