Abstract
This review contains experimental values of polar tensors and generalized atomic polar tensor (GAPT) charges determined since the publication of the polar tensor formulism for infrared intensity interpretation in 1961. GAPT charges, also called mean dipole moment derivatives, for 167 atoms of 67 molecules are discussed and compared with infrared charges also determined completely from experimental intensities. The importance of the charge transfer and polarization dynamic contributions to the GAPT charge are emphasized as they differentiate this charge from most theoretically calculated charges. The inclusion of these dynamic contributions is shown to be necessary to provide adequate numerical descriptions of core electron ionization energy processes. These contributions are expected to be important in studies of chemical reactivity.
Highlights
Atomic charge is the most frequently used molecular parameter containing electronic structure information for predicting chemical reactivities
The infrared charges are conceptually different from the generalized atomic polar tensor (GAPT) charges
E(1s,C): experimental 1s core electron ionization energies; E(rel): relaxation energies; V, (CHELPG) V, (Mulliken) V(zero flux) and V(GAPT): electrostatic potentials owing to neighboring atoms for CHELPG, Mullikan, zero flux and mean dipole moment derivatives, respectively
Summary
Atomic charge is the most frequently used molecular parameter containing electronic structure information for predicting chemical reactivities. As most charges have been determined from molecular wave functions limited basis sets and inexact electronic correlation treatment levels hinder these efforts It does appear as though different charge values owing to alternative definitions are more pronounced than those between quantum chemical and experimental results.[12]. (IR) charges that have been proposed by Zerbi and coworkers.[20,21] Within the point charge model approximation to molecular electronic structure descriptions these can be determined from experimental infrared spectroscopic data for linear and planar molecules These charges are equal to atomic polar tensor (APT) elements of perpendicular vibrations[22] as the molecule must behave as a permanent dipole moment on rotation.[23] As such, these derivatives are comparable to static atomic charges. It is not necessary initial reading for those essentially interested in atomic charges that are discussed in the section immediately after the polar tensor methodology
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