摘要:

Second-order perturbation solutions of the spin hamiltonian

ISSN:0026-8976    

DOI:10.1080/00268977400102451

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The nature of paramagnetic centres trapped in X-irradiated Na2SO4single crystals containing chlorine as impurity has been determined from E.S.R. measurements both at room and liquid nitrogen temperatures. ClO3, ClO2, SO4-and O3-are the paramagnetic centres identified. ThegandAparameters of ClO3change considerably between 298 K and 77 K. Thus the parameters of ClO3obtained at 298 K aregxx= 2·0123,gyy= 2·0143,gzz= 2·0206 G and those of theA-tensor areAxx= 97,Ayy= 100 andAzz= 112 G. The parameters obtained for the same centre at 77 K aregxx= 2·0132,gyy= 2·0173,gzz= 2·0073 G and those of theA-tensor areAxx= 130·6,Ayy= 146·3 andAzz= 181·2 G. The temperature variation of the principal values are determined in the temperature range between 298 K and 77 K. These data can be interpreted on the assumption that ClO3undergoes libration at room temperature, which is frozen out reversibly on cooling. The structure and mechanism of these defects are discussed further.

ISSN:0026-8976    

DOI:10.1080/00268977400102461

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The low temperature thin-film absorption spectra of C6H6, sym-C6H3D3and C6D6in the1B1u←1A1gtransition region are analysed in terms of a 0, 0 crystal-field-induced origin, andv18(e2g),v7(b2g) andv16(e2g) false origins. The 0, 0 +v2(α1g) band is clearly resolved in sym-C6H3D3whilst it merges with 0, 0 +v7(b2g) in C6H6. Recent polarization measurements of the C6H62150 Å band are shown to be consistent with a 0, 0 assignment. The 0, 0 origin is also seen in the fluorescence excitation spectrum of crystal C6H6.

ISSN:0026-8976    

DOI:10.1080/00268977400102471

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The influence of vibronic interactions on the chiroptical spectra associated with pairs of nearly degenerate electronic transitions in chiral systems is examined on a formal theoretical model. We consider the special case in which two nearly degenerate electronic states are coupled by a single non-totally symmetric vibrational mode. Formal expressions are developed for the rotatory strengths of individual vibronic transitions in this coupled system. Calculations based on these expressions are carried out for a large number of parameter sets appropriate for various energy spacings between the unperturbed electronic states, vibronic coupling strengths, oscillator (vibrational mode) frequencies, and electronic rotatory strengths. The calculated results demonstrate the profound influence of vibronic interactions on the sign patterns and intensity distributions within the rotatory strength spectrum associated with the two coupled electronic states. The implications of these results for interpretations of circular dichroism spectra are discussed.

ISSN:0026-8976    

DOI:10.1080/00268977400102481

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Calculations are reported concerning the structure of the anthracene stable dimer. It is shown that the use of an ‘exp-6’ atom-atom potential produces a structure which is definitely not that allowed by the experimental data : this is shown to be due to the absence of any simulation of permanent moment interactions in the atom-atom potentials. A number of conventional methods for calculating the individual terms of the total potential energy are used to estimate the magnitudes of these terms. It is concluded that the resulting relative magnitudes of the individual terms cannot be determined accurately enough to justify the construction of a total potential energy curve. However, by considering the variation of the individual terms with the relative orientation of the two molecules of the dimer, the dominant role of the quadrupole-quadrupole terms in determining the dimer structure is clearly demonstrated.

ISSN:0026-8976    

DOI:10.1080/00268977400102491

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The use of recently determined highly precise rotational constants for various isotopes of formaldehyde and ethylene enables the ground-state average structures to be determined to high accuracy. Harmonic corrections to the inertial constants are calculated using recently determined general harmonic force fields. In the case of formaldehyde, the data enable changes in all three structural parameters due to isotopic mass effects to be determined. For ethylene, only the change in CH bond length on deuteration is well characterized, due to the somewhat lower accuracy in the rotational constants. Using isotopic structural differences transferred from formaldehyde, and supported by calculations, ground-state rotational constants for all deutero isotopes of ethylene are predicted to what is considered to be better than 0·1 per cent reliability.

ISSN:0026-8976    

DOI:10.1080/00268977400102501

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The He(I), He(II) and X-ray photoelectron spectra of iron tricarbonyl butadiene are reported and these measurements, together with the bonding in the complex, are discussed with the aid ofab initioSCF MO calculations. The latter yield a substantial negative charge on the butadiene ligand, and the low energy photoelectron spectra can only be satisfactorily interpreted when deviations from Koopmans' theorem are taken into account by performing RHF calculations on the various low-lying ionic states of the molecule.

ISSN:0026-8976    

DOI:10.1080/00268977400102511

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A statistical mechanical perturbation theory for the pair correlation function and thermodynamic properties of molecular fluids is presented in which the reference potential function is non-spherical. With this choice the short-range molecular repulsive forces can be properly taken into consideration and attractive forces, such as those resulting from electric moments, treated as the perturbation. Calculations are presented for the first-order perturbation term to the Helmholtz free energy due to quadrupolar forces in models of liquid nitrogen and chlorine, and due to dipolar forces in liquid hydrogen chloride. For these calculations the rigid diatomic model and its modification appropriate to heteronuclear molecules were used for the reference potentials. It is found that the lowest-order perturbation terms here are proportional to the second power of the dipole or quadrupole moments, and not the fourth power as had been found previously using a spherical reference potential function. This second-order dependence on the electric moment is especially important in the case of mixtures, where it leads to an explanation for the occurrence of negative azeotropes in binary mixtures of species with quadrupole moments of opposite sign.

ISSN:0026-8976    

DOI:10.1080/00268977400102521

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A dimer radical possessing two anisotropically equivalent phosphorus atoms has been conclusively identified inγ-irradiated trimethyl phosphite, its E.S.R. spectrum consisting basically of four lines due to the large second-order splitting of the central component. In the powder spectrum of theγ-irradiated glass the central features are obscured by overlapping signals from other radicals. However, the downfield (1, 0) feature was clearly revealed by suppressing the formation of the interfering P(OCH3)2radical through the inclusion of methyl bromide in the sample. The E.S.R. spectrum of aγ-irradiated single crystal is very well resolved and three complete sets of lines can be assigned unequivocally to chemically non-equivalent dimers. The spectra of two of the dimers undergo site splitting such that the symmetry elements for each pair of magnetically distinguishable sites are related. In addition, each of the lines belonging to these two dimer spectra is flanked by a pair of ‘spin-flip’ satellites at high microwave power. Chemical and structural evidence strongly suggests that the dimer is the centrosymmetric cation (CH3O)3P-P(OCH3)3/+, the unpaired electron occupying aσ* orbital built from the 3sand 3porbitals of the two phosphorus atoms with ap/shybridization ratio of approximately 2. The chemical non-equivalence of the dimers may result from slight differences in this hybridization ratio.

ISSN:0026-8976    

DOI:10.1080/00268977400102531

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Recentab initiocalculations of the pair interaction between water molecules are claimed to be close to the Hartree-Fock limit. Second virial coefficient calculations for such a Hartree-Fock potential, together with a number of correlation energy corrections, are compared with results obtained from experiment. On the basis of this comparison it is shown that correlation energy terms are needed over the whole range of the interaction and it is not sufficient to directly add dispersion energy terms alone.

ISSN:0026-8976    

DOI:10.1080/00268977400102541

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor