摘要:

The possibility of formulating the symmetry groups of non-rigid molecules (as defined by Longuet-Higgins) as products of subgroups is investigated. For the most general case of non-rigidity, no such formulation is possible. When the non-rigidity results from internal rotation about one or more axes, the molecular symmetry group may be written as a semi-direct product of an invariant torsional subgroup, which is a direct product of cyclic groups, and a ‘frame subgroup’, which is isomorphous with the point group of the ‘frame’ formed by detaching all the nuclei undergoing internal rotation. A correlation table may be drawn up linking the representations of the torsional and frame subgroups with those of the molecular symmetry group. This table may be used to classify the various factors of the molecular wave-function, without the need to perform the tedious construction of the molecular symmetry group.

ISSN:0026-8976    

DOI:10.1080/00268977000101811

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The absorption and magnetic circular dichroism (M.C.D.) spectrum of the IrBr62-ion at room and liquid helium temperature has been studied in the host crystals (NH4)2SnBr6, K2SnBr6and (C2H5NH3)2SnBr6in the region ∼11 000–21 000 cm-1. An interpretation of the spectrum is presented which differs significantly from those suggested previously. In order of increasing energy the allowed bands are assigned to the following ligand-to-metal charge-transfer transitions:Eg″(2T2g)→Uu′(2T1u) (13–14 000 cm-1),Eg″(2T2g)→Eu″(2T2u) (16 800 cm-1), andEg″(2T2g)→Uu′(2T2u) (∼ 18 300 cm-1). Both our absorption and M.C.D. data strongly suggest a Jahn-Teller splitting of theUu′(2T1u) state but contradict a previous suggestion of such a splitting of theUu′(2T2u) state. Consideration of σ—π mixing in thet1u(π + σ) molecular orbital suggests that the ∼17 300 cm-1band arises from the orbitally-forbiddenEg″(2T2g)→Eu′(2T1u) transition. Bands in the 11 000–13 000 cm-1region are assigned to parity-forbidden charge-transfer transitions to states generated by thet1g(π)→t2gexcitation. The fine structure seen at liquid helium temperature in K2SnBr6: Ir4+both in the 14 500 cm-1band and overlying theEg″→Uu′(2T2u) band appears to be associated with parity-forbidden transitions.

ISSN:0026-8976    

DOI:10.1080/00268977000101821

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Le radical tert-butyle obtenu par irradiation γ à 77°kdu chlorure de tertiobutyle peut se présenter sous deux structures différentes. Une forme pyramidale, ayant pour origine les contraintes exercées par le réseau cristallin, et pour laquelle le couplagea13C avec le carbone central est une fonction décroissante de la température. Une forme plane pour laquellea13C croît avec la température. L'étude du radical plan a permis de séparer les contributions relatives des vibrations,a13Cv, et de la polarisation des électrons des couches internes et des liaisons,a13Cpol, à la valeur du couplagea13C. Le résultat obtenu confirme la relative insensibilité dea13CPol, par rapport aux détails des substituants du carbone central, prévue par les calculs de Melchior.

ISSN:0026-8976    

DOI:10.1080/00268977000101831

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The cation radicals of C10F8and several hydrofluoronaphthalenes have been prepared by oxidation with SbCl5/SO2, and their E.S.R. spectra recorded. McLachlan spin-density calculations have been carried out and theQparameters for cation radicals containing fluorine have been determined. Possible explanations for the large fluorine splittings are discussed.

ISSN:0026-8976    

DOI:10.1080/00268977000101841

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Above the solid-plastic transition point, well-resolved E.S.R. spectra are recorded when globular compounds are irradiated by γ-rays. We have studied the free radicals observed after γ-irradiation of 15 derivatives of bicyclo[2,2,1]heptan and eight deuterated homologues. The E.S.R. spectra are analysed; they are consistent with the appearance of a free valence localized on one carbon of the cyclohexane ring (C2 for the hydrocarbons, alcohols and chlorides, C3 for the ketones). We note a strong inequivalence for the β-proton couplings and we explain this by a non-planarity of the three bonds surrounding the free radical centre; the deviation from planarity is estimated to be 20–30°. We also observe strong hyperfine interactions with γ-protons. Such long range interactions are inconsistent with the saturated model where spin density is transmitted by spin polarization of localized bonds; they are specific to the unsaturated character of bicyclic compounds which have an enhanced delocalization of the unpaired electron.

ISSN:0026-8976    

DOI:10.1080/00268977000101851

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The far infra-red (20–400 cm-1) spectra of C6H5F, C6H5Cl, C6H5Br, C6H5I, C6D5Cl, C6D5Br have been recorded for the liquid (300°K) and polycrystalline phases (100°K). The expected lattice spectra and correlation field splittings have been discussed in terms of group theory, and the observed frequency shifts are used to assign the absorption bands to particular motions in the unit cell.

ISSN:0026-8976    

DOI:10.1080/00268977000101861

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Two LCAOMOSCF wave functions for SF6are derived: gaussians,porbitals are employed in a fullab initiocomputation ands,p,dSlater functions in the MZDO treatment. The two sets of results are qualitatively compared and the accuracy of the MZDO procedure is discussed.

ISSN:0026-8976    

DOI:10.1080/00268977000101871

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The thermal conductivity,k, of carbon dioxide is measured by adopting the conductivity column method in the temperature range 100°c to 1075°c. The measurements are taken at various pressures between 12·5 and 50·5 cm of mercury where thekvalues are found to be independent of gas pressure. The estimated accuracy ofkvalues is ±2 per cent and these are correlated within an average absolute deviation of 0·5 per cent by the following quadratic polynomial in temperature (T):

ISSN:0026-8976    

DOI:10.1080/00268977000101881

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Heitler's theory of damping phenomena is used to study the decay of an excited Born-Oppenheimer state through radiative and radiationless transitions. The method allows a straightforward derivation of the decay laws and of the expressions of fluorescence intensity and quantum yield in the large and small molecule limits.

ISSN:0026-8976    

DOI:10.1080/00268977000101891

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The exciton states of the α and β-helical conformations of polypeptides are studied by a new molecular exciton theory. It is found that the α-helical structure shows hypochromism while the parallel and anti-parallel β forms exhibit no remarkable changes. In the α-helical structure the band splitting and the optical rotational strength are reasonably well calculated and the migration velocities for the two exciton states are estimated.

ISSN:0026-8976    

DOI:10.1080/00268977000101901

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor