Derivatives Of Molecular Dipole Moment Research Articles

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.

Theoretical molecular dipole moment derivatives in solid HCN

A Hartree—Fock based self-consistent crystal field method is employed to calculate molecular dipole moment derivatives of HCN in the solid. Qualitative agreement with experiment is obtained for the changes in the stretching normal coordinates molecular dipole moment derivatives, when going from the gas phase to the solid. The molecular polarizabilities are calculated. The latter are translated into the high-frequency contribution to the dielectric constants. Qualitative agreement with experiment is again obtained. Intra-molecular geometry optimization is performed and an elongation of the CH bond by 0.01 Å is obtained. The lattice energy is decomposed into purely electrostatic, Pauli repulsion and dispersion interaction contributions.

Experimental determination of the sign of molecular dipole moment derivatives: an infrared—visible sum frequency generation absolute phase measurement study

We show that the measurement of the absolute phase of the infrared—visible sum frequency susceptibility of a monolayer of molecules of known orientation determines the relative sign of the dipole moment derivative and the polarizability derivative with respect to the normal mode. With the sign of the polarizability derivative well established, we determine the sign of the CH bond dipole moment derivative with respect to the CH stretch for the methyl group of an alkane and for methoxy.

Transferability of dipole moment derivatives: Calculation of absolute rotational contributions for symmetrical molecules

It is shown that Polo's method for the calculation of the D −1 and G −1 matrices can be extended to the calculation of the absolute rotational contributions involved in the molecular dipole moment derivatives in terms of symmetry coordinates. The method applies to both stretching and bending modes. The method is outlined for AB 3 ( C 3 v ) molecules.

Infrared absorption intensities of formyl fluoride

The i.r. absorption intensities of gaseous HCOF and DCOF have been measured under high pressure. The intensity analysis has been carried out, and the derivatives of molecular dipole-moment with respect to a bond stretching or a valence angle deformation have been determined as intensity vectors by the least squares method. Assuming the directions of intensity vectors are those calculated by the CNDO/2 or INDO method, their magnitudes have been determined as follows: a CH = − 0.22, a CO = − 2.90 and a CF = − 5.02( D/Å). Above values are close to those of intensity vectors of unsaturated fluorocarbons. The effect of π electrons on the intensity vectors is briefly discussed.

The optical and spectroscopic properties of the sulfate ion in various crystalline environments

The electronic polarizability components of the sulfate ion in LiKSO4, KNaSO4, K2SO4, Na2SO4, and K2Mg2(SO4)3 were calculated from the optical refractive indices using a point dipole model. The values obtained were discussed in terms of the immediate crystalline environment of the sulfate ion. The frequencies of the transverse and longitudinal internal optic modes were measured by polarized Raman scattering experiments and estimated from near-normal incidence reflectivity spectra. The frequency data were analyzed in a molecular dipole model formalism with static crystal field frequencies and molecular dipole moment derivatives of the internal modes of the sulfate ion being reported and discussed.

Infrared absorption intensities of methane and fluoromethanes

The i.r. absorption intensities of methane and its deutero- and fluoro-derivatives; CH 4, CD 4, CH 3D, CHD 3, CH 2D 2, CF 4, CH 3F, CHF 3, and CDF 3, have been measured under high pressure. The intensity analysis has been carried out and the derivatives of molecular dipole moment with respect to a bond length or a valence angle have been determined as intensity parameters by the least squares method. The rotational correction required for the intensity consideration on a non-totally symmetric vibration of dipolar molecules is discussed briefly. For each molecular species the converged values of the parameters have been compared with the calculated ones by the CNDO/2 and INDO methods, and the most plausible solutions have been determined.

On surface preparation and measurement of niobium used in high-frequency cavities

The i.r. absorption intensities of methane and its deutero- and fluoro-derivatives; CH4, CD4, CH3D, CHD3, CH2D2, CF4, CH3F, CHF3, and CDF3, have been measured under high pressure. The intensity analysis has been carried out and the derivatives of molecular dipole moment with respect to a bond length or a valence angle have been determined as intensity parameters by the least squares method.The rotational correction required for the intensity consideration on a non-totally symmetric vibration of dipolar molecules is discussed briefly. For each molecular species the converged values of the parameters have been compared with the calculated ones by the CNDO/2 and INDO methods, and the most plausible solutions have been determined.

Electrical anharmonicity in vibrating systems containing mechanical anharmonicity due to the relaxation of the molecular electronic charge distribution

The contributions of the relaxation of the molecular electronic charge distribution on vibration to the first and second molecular dipole moment derivatives with respect to a vibration coordinate are calculated.

On the Theoretical Calculation of Vibrational Frequencies and Intensities of Polyatomic Molecules; H3+, H2D+, HD2+, and D3+

A straightforward method is described for calculating the fundamental vibrational frequencies and intensities for a polyatomic molecule starting with a theoretically obtained potential energy surface and associated electronic state wavefunction. Given the latter two quantities, this method is much easier to carry out than the common reverse problem of predicting force constants from observed frequencies and molecular dipole moment derivatives from absolute intensities. The proposed method can be programmed easily and generally to handle any polyatomic system for which a theoretical energy surface and electronic-state wave-function are available. An application to H3+ and its isotopic counterparts is described.