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|Type:||Artigo de periódico|
|Title:||Atomic mean dipole moment derivative and anisotropic contributions to molecular infrared intensity sums|
de Oliveira, AE
|Abstract:||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.|
|Editor:||Amer Chemical Soc|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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