INFRARED INTENSITIES, ATOMIC CHARGES, AND DIPOLE-MOMENTS IN THE FLUOROETHANE SERIES USING ATOMIC POLAR TENSOR ANALYSIS

To gain insight into the interpretation of the atomic polar tensors (A PT) in the series of fluoroethanes, the fluorine, carbon, and hydrogen APT components P-alpha(ss') were calculated, in the inertial-axes coo rdinate system, and examined by determining the mean dipole derivative s (p) over bar(c), the King effective atomic charges chi(alpha), and A PT anisotropies beta(alpha). From this, relationships between chemical bonding environment and (p) over bar(alpha) terms are clearly discern ible, with the carbon-atom charges exhibiting a labile response to the degree and form of fluorine substitution. We examine the dependence o f the total absolute infrared intensities, as predicted by the APT sum rules, on the degree of fluorine substitution and molecular structure for the entire set of fluoroethanes. Finally, dipole-moment component s were calculated (i) directly from ab initio methods at the MP2/6-31G * level, (ii) from the P-alpha(ss') terms, and (iii) as the first mom ents of the (p) over bar(alpha) atomic charges at the nuclear equilibr ium positions, and a detailed comparison was made.