The development is described of a basis set of moderate size optimized for the computation of the dipole polarizability of reasonably large molecules consisting of hydrogen and p-block elements up to iodine. The mean polarizability, polarizability anisotropy and dipole moment for hydrides of the first four rows of the periodic table, obtained at both the SCF and MP2 levels, are compared with those obtained using the previously developed 6–31 G(+ sd + sp) basis set, as well as larger basis sets, and with experiment. For the series of diatomic halogens, X2, and the halomethanes, CH3X (X = F, C1, Br, I), electric properties are obtained in excellent agreement with those resulting from use of larger basis sets, and also with experiment.

Accurate prediction of static dipole polarizabilities with moderately sized basis sets

Coupled Hartree–Fock perturbation theory has been applied to evaluate the first hyperpolarizability in the molecules H2O, NH3, CH4, and CO. A group‐theoretical approach has been employed, which makes it possible for a reduced file of symmetry distinct two‐electron integrals to be processed at each iteration with reduced computer efforts. Several very large basis sets, including up to 4f functions on the heavy atom and 3d on hydrogen, have been retained, which yield SCF energies, dipole moments, polarizabilities, and first hyperpolarizabilities very near to the corresponding HF quantities. Except in the case of CO, large discrepancies with respect to experimental data have been found.

On the theoretical determination of molecular first hyperpolarizability

Frequency-dependent hyperpolarizabilities of haloforms from ab initio SCF calculations

A previously developed interacting segment model [ISM—see J. Chem. Phys. 67, 2109 (1977)] is applied to a full‐scale treatment of the electric dipole moments, isotropic and anisotropic polarizabilities, and hyperpolarizabilities of a series of 12 halogenated methane molecules CXnY4−n(X,Y = H,F,Cl; n = 0–4). The ISM scheme enables the molecular properties considered to be fitted in terms of a set of ’’bare’’ electric tensor parameters for each bond, which are modified (’’dressed’’) by intramolecular electrostatic interactions. The computed results of the ISM scheme, and of a corresponding interaction‐free bond additivity model, are discussed in relation to the following: choice of geometric and bond parameters, quality of fit to experimentally determined molecular and bond properties, and predictive potential and general physical validity of the model. It is concluded that the ISM approach represents a substantial improvement over simple bond additivity as a basis for understanding molecular electric tenso...

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An interacting segment model of molecular electric tensor properties: Application to dipole moments, polarizabilities, and hyperpolarizabilities for the halogenated methanes

Constrained anisotropic dipole oscillator strength distribution techniques are discussed and applied to obtain reliable results for a wide variety of the anisotropic and isotropic dipole properties of H2 and N2. These include the dipole oscillator strength sumsS
k, k=2, 1, −1/2(−1/2) −2, −3, −4, ..., the logarithmic dipole sumsL
k and mean excitation energiesI
k, k=2(−1) − 2, and, as a function of wavelength, the dynamic polarizability and the associated anisotropy, the total depolarization ratio, the Rayleigh scattering cross section, and the Verdet constant. The anisotropic components of the DOSD for a molecule are obtained from a given recommended isotropic DOSD by using a constrained least squares procedure and a series of known anisotropic constraints. Assuming that sufficient input is available, the constrained DOSD approach used in this paper is the only available method for the reliable evaluation ofall the relevant anisotropic and isotropic dipole properties for a wide variety of atoms and molecules.

Constrained anisotropic dipole oscillator strength distribution techniques, and reliable results for anisotropic and isotropic dipole molecular properties, with applications to H2 and N2*

The static Kerr constants of eight substituted methanes in the gas phase have been measured by a low‐frequency null technique. Combining these results with gas phase depolarization ratio measurements we show that the hyperpolarizability contributions to the Kerr constant are small except for CH3F. The magnitudes of the hyperpolarizabilities obtained are in good agreement with the values obtained from second harmonic generation measurments. In the case of nitromethane the electric birefringence and depolarization ratio measurements are combined to obtain the three principal values of the polarizability tensor.

L. W. Buxton

Papers

Kerr constants, depolarization ratios, and hyperpolarizabilities of substituted methanes