Quantum theory atoms in molecules charge-charge flux-dipole flux models for the infrared intensities of benzene and hexafluorobenzene.

The infrared fundamental intensities of benzene and hexafluorobenzene have been calculated at the MP2/6-311++G(3d,3p) level. The theoretical values are in excellent agreement with the averaged experimental C(6)H(6) results having a rms error of 15.3 km mol(-1). However, the theory badly underestimates the CF stretching and ring deformation intensities of C(6)F(6) having an overall rms error of 141 km mol(-1). The theoretical results confirm the dipole moment derivative signs previously attributed on the basis of the comparison of C(6)H(6) and C(6)D(6) derivatives and semiempirical molecular orbital results. A quantum theory atoms in molecules charge-charge flux-dipole flux interpretation of the theoretical results shows that electronic density changes for out-of-plane vibrations can be explained using a simple bond moment-rehybridization moment model proposed many years ago. However, these changes were found to be much more complicated for the in-plane vibrations involving important charge flux and dipole flux contributions for both molecules as well as contributions from the displacement of equilibrium atomic charges for hexafluorobenzene.

Quantum theory of atoms in molecules charge-charge flux-dipole flux models for the infrared intensities of X(2)CY (X = H, F, Cl; Y = O, S) molecules.

The molecular dipole moments, their derivatives, and the fundamental IR intensities of the X2CY (X = H, F, Cl; Y = O, S) molecules are determined from QTAIM atomic charges and dipoles and their fluxes at the MP2/6-311++G(3d,3p) level. Root-mean-square errors of +/-0.03 D and +/-1.4 km mol(-1) are found for the molecular dipole moments and fundamental IR intensities calculated using quantum theory of atoms in molecules (QTAIM) parameters when compared with those obtained directly from the MP2/6-311++G(3d,3p) calculations and +/-0.05 D and 51.2 km mol(-1) when compared with the experimental values. Charge (C), charge flux (CF), and dipole flux (DF) contributions are reported for all the normal vibrations of these molecules. A large negative correlation coefficient of -0.83 is calculated between the charge flux and dipole flux contributions and indicates that electronic charge transfer from one side of the molecule to the other during vibrations is accompanied by a relaxation effect with electron density polarization in the opposite direction. The characteristic substituent effect that has been observed for experimental infrared intensity parameters and core electron ionization energies has been applied to the CCFDF/QTAIM parameters of F2CO, Cl2CO, F2CS, and Cl2CS. The individual atomic charge, atomic charge flux, and atomic dipole flux contributions are seen to obey the characteristic substituent effect equation just as accurately as the total dipole moment derivative. The CH, CF, and CCl stretching normal modes of these molecules are shown to have characteristic sets of charge, charge flux, and dipole flux contributions.

QTAIM charge-charge flux-dipole flux models for the infrared fundamental intensities of difluoro- and dichloroethylenes.

A quantum theory of atoms in molecules (QTAIM) charge-charge flux-dipole flux (CCFDF) decomposition of the MP2/6-311++G(3d,3p) level molecular dipole moment derivatives is reported for the cis-, trans-, and 1,1-difluoroethylenes and the cis- and trans-dichloroethylenes. Although the dipole moment derivatives and infrared fundamental intensities calculated at the MP2 level are overestimated for high-intensity bands corresponding to CF and CC stretching vibrations, the overall agreement is good with a root-mean-square (rms) error of 19.6 km mol-1 for intensities ranging from 0 to 217.7 km mol-1. The intensities calculated from the QTAIM/CCFDF model parameters are in excellent agreement with those calculated directly by the MP2/6-311++G(3d,3p) approach with only a 1.8 km mol-1 rms error. A high negative correlation (r=-0.91) is found between the charge flux and dipole flux contributions to the dipole moment derivatives. Characteristic values of charge, charge flux, and dipole flux contributions are found for CF, CCl, and CH stretching derivatives. The CH stretching derivatives provide especially interesting results with very high charge flux and dipole flux contributions with opposite signs. The charge, charge flux, and dipole flux contributions are found to be transferable from the cis to the trans isomers providing accurate predictions of the theoretical trans intensities with rms errors of 8.6 km mol-1 for trans-difluoroethylene and 5.9 km mol-1 for trans-dichloroethylene.

QTAIM charge-charge flux-dipole flux models for the infrared fundamental intensities of the fluorochloromethanes.

The molecular dipole moments, their derivatives, and the fundamental IR intensities of the fluoro-, chloro-, and fluorochloromethanes are determined from QTAIM atomic charges and dipoles and their fluxes at the MP2/6-311++G(3d,3p) level. Root-mean-square (rms) errors of 0.01 D and 5.6 km mol(-1) are found for the dipole moments and fundamental IR intensities calculated using QTAIM parameters when compared with those obtained directly from the MP2/6-311++(3d,3p) calculations and 0.04 D and 23.1 km mol(-1) when compared with the experimental values. Charge, charge flux, and dipole flux contributions are calculated for all the normal vibrations of these molecules. A large negative correlation coefficient of -0.92 is calculated between the charge flux and dipole flux contributions and indicates that electron transfer from one side of the molecule to the other during vibrations is accompanied by relaxation with electron density polarization in the opposite direction. The CF, CCl, and CH stretching normal modes of these molecules are shown to have characteristic sets of charge, charge flux, and dipole flux contributions. Although the FCF and ClCCl deformation normal modes can also be discriminated from one another based on the sizes and signs of these contributions, some HCH deformations have contributions that are similar to those for some of the ClCCl deformations.