摘要:

The internal energyUMCof crystalline Ar, Kr and Xe has been calculated by the Monte Carlo method, using the latest available potentials including contributions from three-body forces and quantum corrections. The values ofUMCare in excellent agreement with experimental values for the cohesive energy. Similar calculations for a system of 107 particles on 108 lattice sites lead to values of the energy to form a Schottky defect (u1) in these rare-gas crystals. We have also shown that in kryptonu1depends on temperature. Existing data for the temperature dependence of the expansivity and lattice parameter for Ar and Kr have been re-analysed by making use of the calculated values ofu1and values of the non-configurational entropy change on forming a vacancy (s1) have been evaluated for Ar and Kr. These values ofu1ands1are compared with previous experimental and theoretical results.

ISSN:0026-8976    

DOI:10.1080/00268977700101491

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Measurements of the differential scattering cross section for thermal neutrons by heavy water (D2O) have been made for a temperature range 11 to 79°C. A systematic change in the diffraction pattern is observed and the position of the first peak is found to vary linearly with temperature. It is shown that the difference functions corresponding to the temperature changes are insensitive to the experimental and analytic corrections which are applied to the cross-section data and may be used to give information of the structural changes in the liquid by use of Fourier transform methods. The results are consistent with information derived from X-ray diffraction data and show that hydrogen-bond breaking plays an important role in the structural changes which occur as the temperature is raised.

ISSN:0026-8976    

DOI:10.1080/00268977700101501

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Rayleigh scattering of photons with λ=0·86 Å was applied to liquid glycerol atT=-16·5°C. Using the Mössbauer effect, the width and intensity of the quasi-elastic line as well as the inelastic scattering intensity were measured for momentum transfers between 0·6 Å-1and 4·2 Å-1. A model of the molecular motions is developed in order to analyse the results quantitatively. It comprises the molecular structure factor, a radial distribution function for the centres of mass, random-walk diffusion of the centres of mass and of the molecular orientation, and a high frequency motion; translation-rotation coupling is assumed to produce a common jump time. The results are compared with other experiments, especially N.M.R. relaxation.

ISSN:0026-8976    

DOI:10.1080/00268977700101511

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Basis set expansion by inclusion ofsandp-type gaussian functions centred on bond axes is shown to be effective in accounting for electronic relaxation due to correlation effects in molecular wavefunctions of diazene. This study demonstrates the effective correlating role of bond functions and so extends their established role as polarization functions. Extensive bond-function optimization at the CEPA level in diazene indicates that more restricted optimizations may be adequate in further studies.

ISSN:0026-8976    

DOI:10.1080/00268977700101521

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The triplet kinetics of glyoxal-h2and -d2neat crystals have been studied by the method of microwave-saturation recovery and microwave-induced delayed phosphorescence. In all cases studied the spin level closely associated with the carbonyl direction is the most radiative. The populating rates, however, show a rich diversity among the variousx-traps. This is interpreted by having minute distortions of the trap-molecules out of planarity. A large spin-dependence on the deuterium effect of non-radiative decay is reported and an explanation is suggested. A resolved proton hyperfine structure is observed for glyoxal-h2at zero field. Preliminary results on zero-field proton ENDOR are presented.

ISSN:0026-8976    

DOI:10.1080/00268977700101531

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The ODMR spectra of biacetyl in neat crystals and in 3-methylpentane glass have been analysed. Several discrete sites exist in the glass medium but onex-trap dominates in neat crystals. Triplet kinetic studies have been made on the biacetylx-trap. Thez-level is pre-eminent in radiative and total decay, but they-level receives a substantial portion of the triplet population, resulting in a spectacular spin polarization on ‖y>. The orientations of the principal magnetic fine-structure axes relative to the molecular framework have been determined using optically detected high-field E.P.R. They-axis is found to be out-of-plane and thez-axis lies approximately along the C=O direction. This observation is in disagreement with a recent calculation by Leclercqet al.A case is made establishing the origin of the ‘strong green’ emission and our ODMR signals as a biacetylx-trap instead of impurities, as previously suggested by Brand and Mau. The implications of these findings to the photophysics of biacetyl and other α-dicarbonyls are discussed.

ISSN:0026-8976    

DOI:10.1080/00268977700101541

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The algorithm of Evans and Watts [1] is used to calculate shear viscosity, bulk viscosity and thermal conductivity of dilute gases modelled by diatomic Lennard-Jones potentials. The results are given in reduced form as a function ofT* andR* (R* = 0·2, 0·3 and 0·5). They can be used to give the transport coefficients of any homonuclear diatomic modelled by a diatomic Lennard-Jones (12, 6) potential, provided that the mass and force centres are assumed to be coincident. In applying the results to nitrogen it is found that the effective pair potential of MacRuryet al.[2] predicts dilute gas transport coefficients in agreement with experiment for the temperature range 200 to 600 K. It is shown that the three diatomic Lennard-Jones potential parameters for nitrogen can be determined by a joint fit of second virial and bulk viscosity data. The fitted value ofR* is 0·285±0·03, showing that to this level of accuracy the diatomic Lennard-Jones pair and effective pair potentials for nitrogen are consistent.

ISSN:0026-8976    

DOI:10.1080/00268977700101551

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Experimental and theoretical photo-absorption and high energy inelastic electron scattering cross sections, together with refractivity and sum rule constraints, are used to construct the non-relativistic dipole oscillator strength distribution (DOSD) for ground-state CH4. The DOSD is used to evaluate a number of useful dipole oscillator strength sums. For example, these results give the mean excitation energies (estimated error <1 per cent) associated with the Lamb shift and the stopping and straggling of fast charged particles in methane. Results are also given for all the parameters needed to evaluate the total cross section for the inelastic scattering of fast charged particles by CH4in the Bethe-Born approximation. The DOSD is also used to evaluate the molar refractivity, as a function of wavelength, in the ultra-violet and visible spectral region, and to obtain an accurate result (estimated error <1 per cent) for the orientation averaged dipole-dipole dispersion energy constant,C6, for the CH4-CH4interaction. Experimental band intensities are used to evaluate the infra-red contribution to bothC6(CH4-CH4) and the dipole polarizability of methane. Finally combination rule values ofC6(CH4-B), for B=H2, N2, O2, NH3, H2O, NO, N2O and He are obtained by usingC6(CH4-CH4) and accurate literature values forC6(B-B).

ISSN:0026-8976    

DOI:10.1080/00268977700101561

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Nous avons analysé un spectre haute résolution (0,017 cm-1) de la bandev1+v3de34SO2. 438 transitions ont été identifiées, conduisant à un centre de bande à 2475,829±0,001 cm-1; 1'écart standard entre fréquences observées et calculées est de 0,001 cm-1.

ISSN:0026-8976    

DOI:10.1080/00268977700101571

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The solid-state X-ray photoelectron spectrum of benzene is compared to gas-phase results and interpreted with the aid of theoretical models of its electronic structure.

ISSN:0026-8976    

DOI:10.1080/00268977700101581

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor