摘要:

The diagrammatic many-body perturbation expansion is used to calculate potential curves for the X1∑+state of the hydrogen fluoride molecule. Two reference hamiltonian operators are considered and for each of these the energy is evaluated through third order, [2/1] Padé approximants are constructed and upper bounds determined. The quality of the resulting potential curves is assessed by calculating spectroscopic constants. It is shown that the use of shifted denominators leads to inferior convergence properties.

ISSN:0026-8976    

DOI:10.1080/00268977800100011

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Electro-optical experiments on several exciplexes of 9,10-dicyanoanthracene and of N,N-dimethylaniline are reported. It is found that the exciplex fluorescence is polarized parallel to the molecular planes of donor and acceptor. Dipole moments of the fluorescent state are obtained and their relatively small values indicate the pronounced locally excited character of the fluorescent state of these exciplexes. Molecular orbital calculations on the hexamethylbenzene-9,10-dicyanoanthracene exciplex confirm this interpretation. The polarization of the exciplex fluorescence is compared with the polarization of charge-transfer transitions in electron donor-acceptor complexes.

ISSN:0026-8976    

DOI:10.1080/00268977800100021

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Instability conditions of the restricted Hartree-Fock (RHF) solutions for the triplet state are investigated in connection with the orbital degeneracy of the H4system of theD4h,TdandD3hsymmetries. The relative stabilities of the RHF solutions and of the solutions obtained from the instability conditions are discussed. The correlation effects involved in the ground Hartree-Fock solutions are also discussed systematically. It is shown that the instability conditions of the RHF solutions are useful in investigating the correlation effects for the triplet species as well as singlet and doublet species.

ISSN:0026-8976    

DOI:10.1080/00268977800100031

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Electron spin polarization (CIDEP) in free radicals created by reaction of a photo-generated triplet is transmitted, if reaction occurs within their spinlattice relaxation time, along a reaction pathway to secondary radicals. The time-dependence of the E.S.R. signal from the secondary species, obtained at a specific magnetic field, is analysed for periods of time of the order of its relaxation time after the photolysis flash that creates the triplet. It is shown that the relaxation times of the secondary radical can be obtained, thereby greatly increasing the variety of radicals whose relaxation may be studied by rapid-response E.S.R. methods. The relative rates of reaction of a given primary radical with diverse substrates are obtained from measurements of the polarization observed in the secondary species in various solutions.

ISSN:0026-8976    

DOI:10.1080/00268977800100041

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Differential cross sections have been measured for Na scattered by the tetrahedral molecules SiCl4, C(CH3)4, Si(CH3)4and Sn(CH3)4in the thermal energy range. Due to the high velocity resolution (Δg/g≈4 per cent) the rainbow structure with primary and at least one secondary rainbow has been resolved. The broadening and quenching of this structure has been used for the determination of the anisotropy of the interaction potential. The corresponding calculations are based on two different formulations of the sudden approximation. It is observed that due to a compensation of repulsive and attractive forces the rainbow scattering determines an effective anisotropy, αeff, which is found to increase for the tetramethyl molecules from 0·2 to 0·7 with increasing size of the central atom, whereas the value for SiCl4is 0·9 in contrast to the behaviour of other tetrachlorides.

ISSN:0026-8976    

DOI:10.1080/00268977800100051

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

An approximate partitioning procedure is presented which allows theN-state problem to be discussed in terms of unitary solutions of smaller problems. The approximation strategy is a generalization of methods previously investigated numerically for two and three-state problems. The method may well be more general, but the particular application intended at present is to transitions arising from avoided-crossing problems in atomic collisions.

ISSN:0026-8976    

DOI:10.1080/00268977800100061

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The components of the tensors σ(1)and σ(2)which describe respectively the linear and quadratic electric field dependence of the nuclear magnetic shielding have been computed for the hydrogen molecule using SCF perturbation theory with an extended basis set which includes s-, p- and d-orbitals on both nuclei. The calculated components of σ(1)are only slightly affected by the incorporation of d-orbitals unlike those of σ(2)which are altered quite markedly. For the mean shielding the present results provide an interesting comparison with the results of other theoretical and experimental studies.

ISSN:0026-8976    

DOI:10.1080/00268977800100071

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Theoretical calculations on the molecules S4N4H4and F4S4N4were made using the SCF-Xα-SW and CNDO/BW methods. In the SCF-Xα-SW method the parameterization with overlapping spheres gave better orbital energies than the parameterization with touching spheres. The eigenvalues and point charges calculated with the SCF-Xα-SW overlap parameterization were in excellent agreement with those calculated with the CNDO/BW method. In the SCF-Xα-SW method, d-orbitals were found to have an insignificant effect on the eigenvalues and point charges. The (CNDO-BW) Localized Molecular Orbitals, LMO's, are highly localized, and give bent SN bonds with a bond order of 1. The two different bond SN distances in F4S4N4are due to hybridization changes at the suphur and nitrogen atoms.

ISSN:0026-8976    

DOI:10.1080/00268977800100081

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The Dyson equation for the one-body Green's function is solved, in a finite basis representation, using an approximated optical potential derived from its functional derivative expression. Some undesirable features of this approximation are discussed and different techniques used to carry out the computations are examined.

ISSN:0026-8976    

DOI:10.1080/00268977800100091

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The isotropic Compton profilesJ(q) of H2+(2Σg+) and H2(1Σg+) are accurately evaluated in the impulse approximation by employing the exact Born-Oppenheimer wavefunction for H2+and both SCF and correlated (CI) wavefunctions expanded in elliptical coordinate basis functions for H2. For H2, the values ofJ(q), computed using the CI wavefunctions of Davidson and Jones and Hagstrom and Shull, agree well with those obtained from the LCAO-CI wavefunction of B. Liu. The discrepancy between theory and experimental data from X-ray scattering remains, but much better agreement is found with recent high-energy electron-scattering measurements. For H2+, the present results cast doubt on some results reported earlier for the momentum distribution. Experimental measurements are needed to enable comparison with the accurate values reported here for the Compton profile.

ISSN:0026-8976    

DOI:10.1080/00268977800100101

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor