摘要:

A general description of linear optical birefringence effects is presented in terms of the effect of forward scattering on the photon polarization density matrix. The approach enables explicit statements to be given for the polarization changes involved in any linear birefringence phenomenon in terms ofRmatrix elements between plane-polarized base states. Expressions in terms of molecular quantities are listed for theRmatrix elements involved in some typical natural and induced birefringence effects. This description of birefringence is related to the infinitestimal unitary transformations of the density matrix and rotations in Poincaré space.

ISSN:0026-8976    

DOI:10.1080/00268977000100781

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The extension of the polarization density matrix description of optical birefringence phenomena involving multiple interactions between molecules and the electromagnetic field is described. This extension of the previous theory [1, 2] enables non-linear phenomena to be incorporated consistently into the description of birefringence.

ISSN:0026-8976    

DOI:10.1080/00268977000100791

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Second-order, iterative analyses of the P.M.R. spectra of 15 different unsubstituted, condensed, benzenoid hydrocarbons are reported; all the spectra dealt with have been obtained in a common, isotropic solvent (CCl4), and the chemical shifts they afforded have, where solubility permitted, been individually extrapolated to infinite dilution. More coupling constant data have been derived to test an earlier empirical equation, and discrepancies for overcrowded protons, observed previously, are confirmed. Dilution effects are discussed and it is concluded that a systematic comparison of experimental and theoretically calculated chemical shifts can be made reliably only when the experimental shifts have all been obtained by iterative, second-order analysis at (or near) infinite dilution, in a common, isotropic solvent.

ISSN:0026-8976    

DOI:10.1080/00268977000100801

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The McWeeny ‘ring current’ theory is tested critically against a set of consistent, accurate experimental chemical shifts for 85 protons in 16planarunsubstituted condensed benzenoid hydrocarbons, and a regression equation is derived relating quantities calculated from the theory to experimentalτvalues for the non-hindered protons. Systematic deviations of different types of protons from this line are discussed, as also are sigma-bond anisotropy effects and discrepancies observed for overcrowded protons. Some of the assumptions about the geometry of planar benzenoid hydrocarbons normally made in these calculations are relaxed. The McWeeny theory gives a good account of the chemical shifts of non-hindered protons in planar molecules, and the predictions of the theory are not significantly altered if the calculations are based on experimental x-ray geometry. Sigma-bond anisotropy effects are unimportant for non-hindered protons, and, at most, make only a partial contribution to the down-field shifts of hindered ones.

ISSN:0026-8976    

DOI:10.1080/00268977000100811

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The method of McWeeny for estimating magnetic effects due toπelectrons in condensed, benzenoid hydrocarbons is applied to calculate the 97 distinct ‘ring currents’, and sigma ratios (H′/H′benzene) for the 219 chemically-non-equivalent protons in the 21 planar hexacyclic benzenoid hydrocarbons which have been synthesized. Trends in the ‘ring currents’ and sigma ratios are discussed; the ‘ring currents’ are useful for culculating diamagnetic anisotropies, and the sigma ratios can be converted to calculated chemical shifts by use of a previously established empirical equation. These shifts are expected to be of use in assigning signals in the experimental high-resolution P.M.R. spectra of these molecules.

ISSN:0026-8976    

DOI:10.1080/00268977000100821

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

A theory of weak intermolecular interactions is presented which indicates how association in the liquid state can manifest itself in vibration spectra. The theory is applied in this case to CHCl3and CFCl3. The calculations predict which bands are most sensitive to the effects of intermolecular interaction. Previous experimental observations on the behaviour of thea1vibrations of these molecules are reproduced. The calculations also predicted new features in the behaviour of the degenerate vibrations which were confirmed experimentally.

ISSN:0026-8976    

DOI:10.1080/00268977000100831

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Axialgtensors and α-hydrogen hyperfine tensors for frozen (CH3)3MĊH2radicals (M = C, Si, Ge, Sn and Pb) have been obtained by computer fit to first derivative E.P.R. spectra. Rotation about the carbon-metal bond is found to be rapid at 77°kexcept for the first in the series, neopentyl radical, which required 140°kfor coalescence of the superhyperfine structure from theγprotons. Theg‖values are constant for the series at 2·0029 (±0·0004), while theg⊥vales are 2·0024, 2·0023, 2·0020, 1·9997 and 1·9938 (±0·0002), in order, from M = carbon to lead. The α-hydrogen hyperfine splittings are essentially constant at 21 oe for the series. Previously reportedγ-hydrogen hyperfine splittings are reflected in the observed line widths. Their values suggest a change in the sign of the spin density onγ-H in the region of germanium. The contact hyperfine splitting of207Pb was found to be 158 oe. This measurement makes available the hyperfine splittings of α atoms in planar π radicals over the entire length of the periodic table for the first time. It is found that a spin-polarization coefficient can be defined which varies by less than a factor of 2 over this range. This coefficient may prove useful in predicting spin densities or hyperfine splittings for heavy atom-substituted radicals. Calculation ofgvalues based on vacant metaldorbitals predicts the observed trends. These calculations allow estimates of the metald-orbital participation in the ground state of the π radical. This mixing coefficient is approximately 1 per cent and is essentially constant from silicon to lead.

ISSN:0026-8976    

DOI:10.1080/00268977000100841

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The 0–0 band of the 2710åsystem ofp-difluorobenzene has been rotationally analysed by the method of band contour analysis. It has been shown to be a typeBband requiring a1B2u–1Agelectronic assignment. The rotational origin is at 36837·9 ± 0·2 cm-1.

ISSN:0026-8976    

DOI:10.1080/00268977000100851

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The method of rotational band contour analysis has been applied to the 0-0 band of the 2800åsystem ofp-dichlorobenzene. It has been shown to be a typeBband requiring a1B2u–1Agelectronic assignment. The rotational origin of the band is at 35 740·5 ± 0·2 cm-1.

ISSN:0026-8976    

DOI:10.1080/00268977000100861

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The excess volume and Gibbs free energy predicted by the scaled particle theory have been calculated for five binary systems of hard spheres, cubes, tetrahedra, ellipsoids and cylinders where the particles of the mixtures have the same shape but different sizes. At a fixed pressure, the excess volume was dependent on the shape of the particles involved, the temperature, pressure and size ratio of the particle. There appeared to be no equivalent sphere which could describe the equation of state and the mixing properties of the systems of non-spherical particles.

ISSN:0026-8976    

DOI:10.1080/00268977000100871

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor