Paulo H. Guadagnini

Infrared vibrational intensities and polar tensors of CF3Br and CF3I

Abstract The polar tensors of CF 3 Br and CF 3 I determined from experimental intensities are reported. The sign ambiguities in the dipole moment derivatives derived from the intensities give rise to several polar tensor solutions, the most physically significant of which being chosen upon comparison with the results of ab initio molecular orbital calculations. The comparison is made more efficient by projecting the polar tensor space in bidimensional principal component graphs. The carbon mean dipole moment derivatives and effective charges in both molecules are in good agreement with estimates from electronegativity model equations obtained from fluoro- and chloromethane polar tensor data. The sum intensities of the two molecules are in good agreement with values estimated from the G sum rule in which electronegativity model estimations for the effective charges are used. Moreover, the carbon mean dipole moment derivatives of these molecules can be taken as atomic charges in a simple model recently proposed for estimation of atomic 1s core electron energies in molecular environments in which a linear relationship is expected to exist between the charge of the atom and its 1s core electron energy corrected for the electrostatic potential from neighboring atoms. The carbon mean dipole moment derivatives of CF 3 Br and CF 3 I fit very well a previous model regression of the relationship based on values of mean dipole moment derivatives for several halomethanes containing sp 3 carbon atoms.

Multivariate statistical investigation of the effects of wave function modifications on the calculated vibrational frequencies and infrared intensities of CH2F2

Abstract Factorial design calculations for the vibrational frequencies and infrared intensities of CH2F2 are reported. Vibrational frequencies decrease by about 100 cm−1 compared with results obtained from Hartree-Fock wave functions when the second-order Moller-Plesset perturbation is applied. The inclusion of polarization functions increases the stretching frequencies by about 100 cm−1 and the CH2 and CF2 angular vibrations by about 50 cm−1, whereas it lowers the values of the CH stretching frequencies. CH2F2 calculated frequencies, which are found to have similar factorial design effects, also have optimal calculated results for the same wave function. Principal component projections of theoretical frequency and intensity results are shown to provide accurate graphical representations of how well these results agree with the experimental values. The factorial design models and principal component graphs of CH2F2 are found to be very similar to those of CH3F for the calculated frequencies. However, these results are quite different for the calculated infrared intensities.

The correlation of proton affinities with atomic charges and electronegativities for the group 14 to 17 hydrides

Proton affinities for hydrides of formula \documentclass{article}\pagestyle{empty}\begin{document}

Hydration properties of Al3+ ion using empirical ion-water potential by Monte Carlo simulation

\mathrm{AH}^{-}_{n-1}

Core Electron Energies, Infrared Intensities, and Atomic Charges

\end{document} containing the elements A from the second to the fifth period of the periodic table and groups 14 to 17 are predicted at the Hartree–Fock, MP2 and B3LYP levels of theory employing both core potential basis sets and the 3‐21G basis set. The core potential methods perform well when compared with all electron calculations using the 3‐21++G** basis set. The proton affinities of the hydrides containing elements from groups 15 and 16 of the periodic table are more accurate than those with elements from groups 14 and 17. A cancellation of errors appears to occur more completely if the protonated and nonprotonated molecules contain both bond and lone pairs before and after the protonation reaction. Proton affinities correlate nearly linearly with the atomic charges on the hydrogen atoms when these charges are determined by the generalized atomic polar tensor (GAPT) method. This tendency can be associated, in principle, with the group electronegativities as introduced by Iczkowski and Margrave.

A Simple Potential Model Criterion for the Quality of Atomic Charges

Neste trabalho, propriedades de hidratacao do ion Al3+ sao investigadas por simulacoes mecânico-estatisticas de Monte Carlo no ensemble NpT a 298,15 K e 1 atm usando um modelo de potencial efetivo de pares ion-agua cujos parâmetros foram desenvolvidos por meio de busca empirica no espaco de fase configuracional durante o curso das simulacoes para reproduzir dados experimentais da estrutura da primeira camada de hidratacao. Resultados estruturais obtidos a partir das simulacoes para numeros de coordenacao e distâncias ion-oxigenio da agua, correspondentes as camadas de hidratacao primeira e segunda, estao em muito bom acordo com dados experimentais. A entalpia de hidratacao predita a partir deste modelo tambem esta em muito bom acordo com resultados experimentais e e bastante similar ao resultado obtido por Wasserman et al. a partir do modelo de ion hidratado. Contribuicoes de muitos corpos investigadas para um cluster [Al(H2O)6]3+ usando a teoria do funcional de densidade em calculos mecânico-quânticos de primeiros principios fornecem suporte a efetividade do potencial de pares ion-agua desenvolvido quanto aos efeitos de muitos corpos incorporado nos parâmetros ajustados.