摘要:

Calculations of peak ENDOR enhancements as functions of experimental conditions have been carried out for a model π-radical containing a pair of symmetrically equivalent α-protons and a single β-proton using the theory developed by Freed. The results are compared with observations on the 2,6-di-t-butyl-4-cyclohexyl phenoxy radical. There is good qualitative agreement between theory and experiment.

ISSN:0026-8976    

DOI:10.1080/00268977500100271

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Long-range isotropic proton hyperfine coupling in rigid bicyclic systems is investigated using a non-empirical configuration interaction study of an appropriate σ-bonded fragment in conjunction with a semi-empirical description of a particular spin label. The coupling is found to depend on the symmetry of the highest occupied molecular orbital of the spin label and upon the stereochemistry of σ-bonded moiety. Relationships are obtained linking the hyperfine coupling to the adjacent spin density of the label for both cases wherein the highest occupied molecular orbital is either symmetric or anti-symmetric relative to the reflection plane containing the C-H bond. Numerical calculations are carried out for the particular case of the bicyclo-[2.2.1]heptane semidione radical anion wherein the reflection plane contains the γ-CH2group as well as bisecting the molecular orbitals of the spin label.

ISSN:0026-8976    

DOI:10.1080/00268977500100281

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Exact quantum mechanical transition probabilities have been calculated for the collinear F + H2→H + HF reaction by the State Path Sum method. The potential energy surface used is based on theab initioSCF CI surface of Benderet al.For the energy range considered, four product channels are open. Pronounced level inversion is found. The dominant transition is the 3 ←0 one. It has a resonance-like energy dependence which is similar to that for the 2 ←0 transition. The 1 ←0 and 0 ←0 transition probabilities are negligible. These results are compared with those of Wuet al.and Schatzet al.who use semi-empirical LEPS surfaces.

ISSN:0026-8976    

DOI:10.1080/00268977500100291

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The model for electron-transfer kinetics in solution is considered. In one model the appropriate energetic condition for charge transfer is met by a small number of vibration-rotation states in thermal equilibrium with the solution. Collisional activation (CA) between ion in the solution and the solvent is the origin of such states. In another model CA is neglected and the appropriate energy states are regarded as being reached by the fluctuations in the energy of the ion, as a result of its interaction with many surrounding solvent molecules; this is the energy fluctuation (EF) model. The dependence of the charge-transfer rate upon the interfacial potential difference for the two models is outlined, and the differences between the models is discussed.

ISSN:0026-8976    

DOI:10.1080/00268977500100301

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The adsorption isotherms for Kr monolayers on graphite measured by A. Thomy and X. Duval,J. chim. phys.,67,1101 (1970) are transformed into the ‘spreading pressure’ as a function of the number density of adsorbed molecules and compared with the pressure of a two-dimensional Lennard-Jones fluid determined by the molecular dynamics technique. The comparison shows that the mobile-layer model for adsorption fails at low temperatures. The liquid-solid phase transitions in the adsorption monolayer appear at lower densities than in a two dimensional Lennard-Jones fluid and the adsorbed liquid layer is compressible in contrast to the two-dimensional Lennard-Jones liquid.

ISSN:0026-8976    

DOI:10.1080/00268977500100311

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

A representation of theS-matrix for reactive scattering is derived on the basis of the exponential approximation. The theory differs from previous distorted wave studies of reactive scattering by using an adiabatic basis set, defined in a reaction path coordinate system. Trial calculations are reported on H + H2and the results compared with converged close coupling calculations. The comparison shows that the range of applicability of this approximation extends to higher energies when this type of basis is used.

ISSN:0026-8976    

DOI:10.1080/00268977500100321

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Bimolecular nucleophilic substitution at a silicon centre has been investigated by the use ofab initiomolecular orbital theory in an examination of the attack of hydride and fluoride anions upon silane and silyl fluoride, respectively. In particular, the role of polarization functions in determining the magnitude of reaction barriers was explored. The inclusion of diffuse functions in the calculations was necessary in order to correctly describe the anionic species. Comparative calculations were performed for the corresponding carbon systems. It is concluded that the carbon systems show barriers to reaction since their reaction complexes are of higher energy than the reactants, unlike the silicon systems where the reaction complexes are of lower energy. The carbon reaction complexes exhibit elongated bonds to the entering and leaving groups, which is expected from the traditional picture of bimolecular nucleophilic substitution, in contrast to the silicon complexes where only small changes from the reactant bond lengths occur.

ISSN:0026-8976    

DOI:10.1080/00268977500100331

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The Kirkwood expression for the static dielectric constant of a polar substance is extended to non-zero frequencies by a means which avoids the introduction of spherical specimens and the connection between the dipoledipole correlation functions of distinct spatial regions. The procedure is based on a previously derived relation between the dynamic dielectric constant and the current-current susceptibility and on the use of the Callen-Welton theorem to relate the susceptibility to fluctuations. Surface effects are eliminated at the outset by consideration of media which are infinite in extent. A general relation between the long-range dipole-dipole correlations (which fall off as the inverse cube of the distance) and short-range correlations in a specimen composed of non-polarizable molecules is found from a consistency relation. It is shown that the two microscopic relaxation times which result from the existence of but one relaxation time in the dielectric constant correspond to the transverse and longitudinal relaxation times with the longitudinal time being screened relative to the transverse time by the static dielectric constant.

ISSN:0026-8976    

DOI:10.1080/00268977500100341

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The relationship between the momentum representation of the classical phase in action-angle variables and the coordinate representation in cartesian coordinates has terms which are associated with discontinuities in thef2generator of the transformation between the two coordinate systems. The importance of these terms has not been emphasized in some earlier work.

ISSN:0026-8976    

DOI:10.1080/00268977500100351

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

A statistical thermodynamic description of the two-dimensional system composed of non-spherical particles with the pair potential of the Kihara-core type is proposed; thermodynamic functions of fluids are expressed in terms of the integrals over two angles and the shortest distance between envelopes of the respective cores. For the system of the two-dimensional hard convex bodies an average correlation function is defined and used to express the equation of state and the chemical potential of pure fluids. Exploiting the ideas of the scaled particle theory the values of the averaged correlation function at the distance of closest approach are determined as functions of the geometric functionals—areas and the (1/2π)-multiples of the circumferences of convex bodies. The values of the compressibility factor obtained from the proposed theory are compared with the Monte Carlo data for a system of hard ellipses.

ISSN:0026-8976    

DOI:10.1080/00268977500100361

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor