CORE ELECTRON ENERGIES, INFRARED INTENSITIES, AND ATOMIC CHARGES

Carbon 1s electron binding energies determined by X-ray photoelectron spectroscopy and mean dipole moment derivatives obtained from experime ntal infrared intensities are shown to be related through the simple p otential model proposed by Siegbahn and collaborators. The sp(3) carbo n atoms in 13 halomethanes, 2 ethanes, 3 methylacetylenes, cyclopropan e, and ethylene oxide have 1s energies, which, after correction for el ectrostatic potentials from neighboring atoms, are linearly related to the carbon mean dipole moment derivatives, presenting a slope of 15.5 0 +/- 0.29 eV/e. The sp(2) carbons of ethylene, three haloethylenes, a nd three carbonyl compounds also exhibit a linear relationship having a significantly different slope of 17.37 +/- 0.87 eV/e. The sp carbon atoms in acetylenes, cyanides, CO, CS2 CO2, and OCS show a third linea r relationship, with a slope of 18.90 +/- 0.75 eV/e. These slopes are proportional to the inverse atomic radii of sp(3), sp(2), and sp carbo n atoms and according to the simple potential equation can be interpre ted as estimates of Coulomb repulsion integrals involving these hybrid ized orbitals and the 1s core electron orbitals. Two basic assumptions of the potential model are investigated. The effect of relaxation ene rgies on the 1s electron ionization processes is estimated as the diff erence between Delta SCF ionization energies and Koopmans' frozen orbi tal estimates obtained from 6-31G(d,p) wave functions. These results a re compared with values obtained previously from the equivalent cores estimating procedure. Also the conceptual validity of identifying the carbon mean dipole moment derivatives as atomic charges Is discussed w ithin the framework of the charge-charge flux-overlap model.