The infrared fundamental intensities and polar tensor of CF4

Atomic polar tensors of carbon tetrafluoride are calculated from experimental fundamental infrared intensities measured by several research groups. Quantum chemical calculations using a 6-311 + + G(3d, 3p) basis set at the Hartree-Fock, Moller-Plesset 2 and Density Functional Theory (B3LYP) levels are used to resolve the sign ambiguities of the dipole moment derivatives. The resulting carbon mean dipole moment derivative, (p) over bar(C) = 2.051 e, is in excellent agreement with values estimated by a MP2/6-311 + + G(3d, 3p) theoretical calculation, 2.040 e, and by an empirical electronegativity model. 2.016 e. The (p) over bar(C) value determined here is also in excellent agreement with the one obtained from the CF4 Is carbon ionization energy using a simple potential model, 2.059 e. Crawford's G intensity sum rule applied to the fundamental intensities of CH4, CH3F, CH2F2 and CHF3 results in a prediction of a 1249 km mol(-1) intensity sum for CF4 in good agreement with the experimental values of 1328 +/- 37.9, 1208.0 +/- 54.4 and 1194.8 +/- 7.4 km mol(-1) reported in the literature. (C) 2000 Elsevier Science B.V. All rights reserved.5671329133

Atomic mean dipole moment derivative and anisotropic contributions to molecular infrared intensity sums

Atomic anisotropies determined from gas-phase infrared fundamental intensity data for 30 molecules are compared with anisotropies calculated from wave functions obtained with 6-31 +G(d,p) and 6-311 ++G(3d,3p) basis sets at the Hartree-Fock, B3LYP density functional and MP2 electron correlation levels. The discrepancies between the experimental and theoretical anisotropy values are up to 30 times larger than those found for the mean dipole moment derivatives. Although a change in the basis set from 6-31+G(d,p) to 6-311++G(3d,3p) has small effects on the anisotropy values, they are quite sensitive to the inclusion of post-Hartree-Fock electron correlation treatment. Although the calculated results for anisotropies with values <0.7e(2) deviate randomly from the experimental results, calculated anisotropies with higher values tend to overestimate the experimental values. Molecules with double bonds (CH2CF2, COH2, COF2, COCl2, cis-C2H2O2, CO2, CS2, and OCS) are found to have high atomic anisotropies and large anisotropic contributions to the experimental intensity sums, whereas these contributions are much smaller for molecules containing triple bonds. Mean dipole moment derivative contributions are predominant over anisotropic ones for the fluorochloromethanes and fluorine-rich fluoromethanes. These results are interpreted using an atoms-in-molecules charge/charge flux/dipole flux decomposition of the dipole moment derivatives of CO, CO2, CS2, OCS, HCN, C2H2, and C2N2. Large positive weighted charge flux and dipole flux contributions are canceled to a large extent by large negative weighted charge flux-dipole flux interaction terms for all these molecules. Whereas this cancellation is only partial for the double-bonded molecules, it is almost perfect for the triple-bonded ones.108326788679

Simple potential models for carbon 1s ionization energies using infrared mean dipole moment derivatives

Simple potential model relations for experimental carbon Is ionization energies (E(C,1s)) and carbon mean dipole moment derivatives ((p) over bar(C)) obtained from experimentally measured infrared fundamental band intensities are investigated for a diverse group of 29 molecules. Positive and negative correlations of the E(C,1s) values and neighboring atom electrostatic potential contributions, V, with the (p) over bar(C) values result in large variances for the E(C,1s)-V values and excellent potential model fits. MP2/6-311+ +G(3d,3p) level Koopmans' energies are shown to provide the most precise potential model fits with correlation coefficients of 0.9996, 0.9962 and 0.9960 for sp(3), sp(2) and sp hybridized carbon atoms, respectively. Potential models using experimental ionization energies adjusted by HF/6-31G(d,p) level relaxation energies are almost as precise. The slopes of the potential lines obtained using Koopmans' energies or experimental ionization energies adjusted by relaxation energies increase with increasing values of the inverse covalent sp(3), sp(2) and sp radii. Relative electrostatic potentials at carbon nuclei calculated directly from electronic densities of MP2/6-311+ +G(3d,3p) molecular orbital wave functions are shown to be in good agreement with those estimated by mean dipole moment derivatives calculated from the same wave functions. (C) 2000 Elsevier Science B.V. All rights reserved.107321121

Core ionization energies, mean dipole moment derivatives, and simple potential models for B, N, O, F, P, Cl, and Br atoms in molecules

Simple potential models relating experimental 1s electron ionization energies for B, N (sp and sp(3) hybrids), O, and F atoms; 1s and 2p ionization energies for P atoms; and 2s and 2p ionization energies for Cl atoms as a function of their atomic mean dipole moment derivatives determined from experimental gas phase infrared fundamental band intensities a-re reported. Potential models using theoretical Koopmans' energies and generalized atomic polar tensor (GAPT) charges are found to form even more precise models than those using experimental data. This is expected because the potential models depend only on the electronic structures of molecules before ionization takes place and do not take into account relaxation effects. If the experimental ionization energies are adjusted by their relaxation energies, models similar to those obtained using Koopmans' energies are determined, The models permit a simple understanding of substituent effects on core ionization energies in terms of atomic charges in molecules. Most of the potential model slopes investigated are shown to be approximately proportional to the inverse atomic radii of the atom being ionized. Core-valence electron repulsion values inferred from the potential models obtained from experimental data are somewhat smaller than those calculated using Slater orbitals of isolated atoms. The potential model intercepts for Is and 2p electrons are shown to be proportional to the square of the nuclear charge, consistent with their interpretation as core electron ionization energies of neutral atoms. 1s He, Ne, and Ar and 2p Ar, Kr, and Xe core ionization energies obey the linear relationships obtained for the model intercepts. The results suggest that mean dipole moment derivatives obtained from infrared intensities can be interpreted as atomic charges.10691824183

A simple potential model criterion for the quality of atomic charges

The simple potential model has been shown to be useful in relating core electron binding energies measured in the X-ray region with mean dipole moment derivatives obtained from experimental infrared vibrational intensities. The importance of including relaxation corrections to the experimental Is ionization energies of sp, sp(2), and sp(3) hybridized carbon atoms are investigated here. Although relaxation energies obtained from 6-31G(d,p) and 6-311++G(3df,3p) basis sets using Delta SCF calculations show differences of about 1 eV for most molecules studied, relative differences are of the order of 0.1 eV. Exceptions are the CO, CO2, COS, and CS2 molecules where discrepancies are larger. Relaxation energy corrections improve simple potential model fits with mean dipole moment derivatives for all carbon atom models but is most pronounced for the sp hybridized atoms. The simple potential model corrected for relaxation energies is investigated as a criterion for testing the quality of Mulliken, CHELPG, Bader and GAPT carbon atomic charges calculated from MP2/6-311++G(3d,3p) wave functions. The GAPT charges are in excellent agreement with the experimental mean dipole moment derivatives (within 0.067e) and provide superior statistical fits to the simple potential model when compared with those obtained for the ether charges.103254918492

The infrared intensities and polar tensors of the fluorochloromethanes

The polar tensors of CF3Cl, CF2Cl2 and CFCl3 have been calculated using recent measurements of their gas phase infrared fundamental intensities. The polar tensors obtained for CF2Cl2 and CFCl3 are in very good agreement with those obtained previously since the more recent experimental intensity results are in good agreement with those reported earlier. For CF2Cl2 )over bar>(C) = + 1.626, )over bar>(F) = - 0.577 and )over bar>(Cl) = - 0.26e whereas )over bar>(C) = + 1.369, (P) over bar (F) = - 0.478 and )over bar>(Cl) = - 0.297e for CFCl3. However, two sets of significantly different mean dipole moment derivatives are obtained from the experimentally measured intensities of CF3Cl reported by two different laboratories. On the other hand, the differences in the mean derivatives of these two sets are not large enough so that results from electronegativity models, potential models for core ionization energies and quantum chemical calculations at the Moller-Plesset 2 and B3LYP density functional levels are sufficient to indicate which set is the correct one. As such average values of )over bar>(C) + 1.907 +/- 0.178e, )over bar>(F) - 0.590 +/- 0.056e and )over bar> = - 0.139 +/- 0.013e obtained from both sets of polar tensor elements are recommended for the CF3Cl mean dipole moment derivatives. (C) 2001 Elsevier Science B.V. All rights reserved.57225526

Characteristic substituent-shift models for carbon 1s ionization energies and mean dipole-moment derivatives

Characteristic substituent-shift models for carbon mean dipole-moment derivatives are determined for the halomethanes, fluorochloroethanes, and some other small molecules. These models are analogous to those reported earlier for core ionization energies measured by X-ray photoelectron spectroscopy and are to be expected since Siegbahn's simple potential model relates these to mean dipole-moment derivatives obtained from infrared spectral data. Linear models relating carbon 1s ionization energies and mean dipole-moment derivatives to the number of fluorine, chlorine, bromine, and iodine atoms substituting hydrogen atoms in the halomethanes are reported. The regression coefficients in these models are similar to the coefficients for the fluorine and chlorine atoms found in linear models derived for the mean dipole-moment derivatives and carbon 1s ionization energies of the fluorochloroethanes. The signs of the coefficients in the fluorochloroethane model indicate that the alpha carbon becames more positive and the beta carbon more negative upon fluorine substitution for hydrogen. Standard derivative values of -0.52+/-0.05, -0.25+/-0.05, -0.18+/-0.03, -0.17+/-0.03, and -0.01+/-0.01 e are proposed for the fluorine, chlorine, bromine, iodine, and hydrogen atoms of saturated fluorochlorohydrocarbons. Characteristic substituent shifts for Mulliken, CHELPG, and Bader charges of the carbon atoms in these molecules are also investigated.108586687