摘要:

The relative intensities of the ENDOR signals from the α and β-protons in the 2,5-dimethyl-p-benzoquinone radical anion depend markedly on temperature. It is suggested that this behaviour reflects the operation of different relaxation mechanisms for the two types of proton: modulation of the electron-nuclear dipolar interaction by the molecular tumbling for the α-protons and modulation of the contact interaction by internal motion for theβ-protons. These ideas are incorporated into calculations of the peak ENDOR enhancements forS=½,I=½ systems. The ENDOR effect is considered to be due to the change in saturation parameter which arises when the nuclear transition is excited. The lattice-induced transition probabilities and relaxation matrix elements required to model an α-proton are calculated from a relaxation hamiltonian which includes modulation of thegand dipolar tensors and the spin-rotation interaction. For theβ-proton a term to include modulation of the isotropic hyperfine interaction is also included in the relaxation hamiltonian. The calculations give a good qualitative description of the dependence on temperature-solvent viscosity and r.f. power of the ENDOR of the single α andβ-protons in galvinoxyl and in the 2,6-di-t-butyl-4-cyclohexyl radical respectively, and of the comparative behaviour of the α andβ-proton ENDOR in the 2,5-dimethyl-p-benzosemi-quinone anion.

ISSN:0026-8976    

DOI:10.1080/00268977400100121

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A simple approximation based on asymptotic wavefunctions is used to calculate the splitting ΔV(Rc) between the pair of adiabatic potential energy curves that arise from pseudo-crossing of ionic and covalent states of a diatomic molecule at a large internuclear distanceRc. In this approximation, ΔV(Rc) is an exponentially decreasing function ofRcand otherwise depends only on the ionization potential of the donor atom and the electron affinity and atomic radius of the acceptor atom. Results obtained for the H*(2s, 2p) + H(1s)→H++ H-interaction are found to agree well with the ΔV(Rc) derived from spectroscopic data for theB1Σu+excited state of H2and a variational calculation of Kolos and Wolniewicz. Results for the alkali hydride interactions, M + H→M++ H-, agree well with estimates of ΔV(Rc) derived from spectroscopic data for theA1Σ+excited states and a variational calculation of Brown and Shull. Results for the alkali halides agree well with photo-dissociation spectra and with collisional ionization cross sections. The method is also applied in a preliminary way to estimate the entrance-channel interaction involved in the ‘electron-jump’ model for reactions of alkali atoms with halogen molecules.

ISSN:0026-8976    

DOI:10.1080/00268977400100131

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Monte Carlo techniques have been used to obtain pair functions and some thermodynamic functions for a two-dimensional system of particles interacting with a Lennard-Jones 12-6 potential. The results extend from the solid phase to the gas, and are at temperatures both above and below the liquid-gas critical point.

ISSN:0026-8976    

DOI:10.1080/00268977400100141

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The decay function of the electric moment of a dielectric shell is calculated directly. It is shown that this function depends on the initial polarization of the shell, the value assumed by Glarum being correct if the shell was initially polarized by a uniform external field, that used by Fatuzzo and Mason being correct if the shell was initially polarized by a central dipole.

ISSN:0026-8976    

DOI:10.1080/00268977400100151

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Argon viscosity coefficients and spectroscopic constants are calculated for the three-parameter potential of Smith and Thakkar. Good agreement with experiment is found. Parameters for krypton and xenon are determined by fitting to semi-empirical dispersion coefficients and experimental second virial coefficients. Viscosity coefficients for krypton and xenon are calculated as an independent test of the potentials so determined. Agreement with experiment is found to be good. The vibrational structure of the ground state of the krypton and xenon dimers is predicted from these potentials. It is concluded that this potential function is adequate for simultaneous correlation of dispersion, viscosity and second virial coefficients of the Noble gases and the vibrational energy levels of their dimers.

ISSN:0026-8976    

DOI:10.1080/00268977400100161

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A simple level ofab initiomolecular orbital theory with a split-valence shell basis withd-type polarization functions (6–31G*) is used to predict equilibrium geometries for the ground and some low-lying excited states ofAHnmolecules and cations whereAis carbon, nitrogen, oxygen or fluorine. The results are shown to be close to the limit for single determinant wave functions in cases where corresponding computations with more extensive bases are available. Comparison with experimental results also shows good agreement although a systematic underestimation of bond lengths up to 3 per cent is evident. For systems where no experimental data are available, the results provide predictions of equilibrium geometry.

ISSN:0026-8976    

DOI:10.1080/00268977400100171

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The He(I) photoelectron spectra of the isoelectronic series Fe(CO)2(NO)2, Co(CO)3NO and Ni(CO)4are reported and interpreted by means ofab initioSCF-MO calculations. For the nitrosyl complexes it is found that ionization potentials calculated assuming Koopmans' theorem are seriously in error due to the considerably greater orbital relaxation accompanying ionization from metal than from NO valence orbitals. When such allowance is made for orbital relaxation by performing restricted Hartree-Fock (RHF) calculations on the ionic states, the experimental spectra are accurately reproduced and the observed similarity of the spectra of all three molecules is explained.

ISSN:0026-8976    

DOI:10.1080/00268977400100181

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A modified Poisson-Boltzmann equation for symmetrical electrolytes is considered which includes estimates for both the fluctuation potential and the volume term. The equation is solved using a previously developed quasilinearization procedure for 1 : 1 and 2 : 2 electrolytes and the results compared with the Monte Carlo computations. In the 1 : 1 case good agreement is found with the Monte Carlo calculations, the results being on a par with the HNC calculations. In the 2 : 2 case satisfactory qualitative agreement is found with the preliminary findings of the Monte Carlo calculations.

ISSN:0026-8976    

DOI:10.1080/00268977400100191

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A variational wave function for the total spinS= 0 and a spin correlation function are derived for the ground state of long polyenes described by means of the Hubbard hamiltonian using the generalized Hartree-Fock method. A criterion of antiferromagnetic spin structure is discussed. The singlet ground states of long molecules with conjugated bonds are found to be antiferromagnetic.

ISSN:0026-8976    

DOI:10.1080/00268977400100201

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The structure and excess energy of the end region of certain one-dimensional systems are investigated. Fowler's expression for the surface excess energy is found to be exact for a Takahashi system with an ideal, fixed end-point. Exact formulae for the local density and the surface energy are derived and discussed for a system with square-well molecules.

ISSN:0026-8976    

DOI:10.1080/00268977400100211

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor