摘要:

CI calculation with a large basis have been used to calculate the two lowest3Π adiabatic potential energy curves for the title reaction. These potentials have been transformed to diabatic potentials by employing a recipe based on the CI coefficients. Quantum mechanical close coupling calculations in the diabatic basis have produced total and differential cross sections which are in good agreement with experimental data. Full quantum mechanical and Landau-Zener calculations of the total cross section are in fair agreement with recent experimental measures and by small changes to the diabatic potentials can be brought into essentially exact agreement.

ISSN:0026-8976    

DOI:10.1080/00268978600100491

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The relationship between vibrational-memory functions and frequency-dependent intermolecular force-autocorrelation functions is shown by modeling the vibrational-correlation functions from a cumulant-expansion equation and then calculating the memory functions via a generalized Langevin equation. Both the memory functions and force-autocorrelation functions are treated as autoregressive time series. It is shown that there exists a one-to-one correspondence between the frequencies of the force-autocorrelation and memory functions.

ISSN:0026-8976    

DOI:10.1080/00268978600100501

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The reliability of Langevin dynamics simulations is investigated and compared with moelcular dynamics simulations. Liquid Kr at three thermodynamic states was considered and a wide range of solute-solvent ratios analysed. While solute structure is reasonably reproduced, marked discrepancies are observed in the dynamic evolution. The agreement worsens as the solute concentration increases but there is a progressive improvement when the solvent concentration becomes lower. The proposed method enables us to analyse the effects on self-diffusion coefficients of direct and hydrodynamic interactions separately.

ISSN:0026-8976    

DOI:10.1080/00268978600100511

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The electronic absorption spectrum, electronic Raman spectrum of Cs2NaPrCl6, luminescence spectrum of Cs2NaPrCl6and Cs2NaYCl6: PrCl63-, and the excitation spectrum of Cs2NaYCl6: PrCl63-have been studied between room and liquid helium temperatures. Twenty-four transitions from the (3H4)Γ1electronic ground state to excited crystal field components have been observed and assigned from the absorption spectrum. Under excitation in the blue two luminescent states are identified at room temperature and these are assigned to (3P0)Γ1and (3P1)Γ4. Twenty-six (of the expected 29) luminescence transitions from (3P0)Γ1have been observed and detailed assignments are given. The moeity mode and lattice mode vibronic structure have been interpreted in detail, with specific reference throughout to the effects of theOh5→C4h5phase transition in Cs2NaPrCl6. These lead to (i) a splitting and magnetic dipole intensity enhancement of some zero phonon lines, (ii) different lattice vibration structure and (iii) the appearance of further fine structure for moeity mode vibronic origins in Cs2NaPrCl6. In two transitions of Cs2NaYCl6: PrCl63-Fermi resonance leads to appreciable vibronic coupling between electronic levels and these effects are predictably absent in Cs2NaPrCl6. An investigation has been made of the electronic origin intensity due to Pr3+at defect sites in both materials. The failure of crystal field theory to predict the energy level scheme, and the MD intensities of some transitions is discussed. A comparison has been made with the luminescence and excitation spectra of Cs2NaYBr6: PrBr63-. The fourth and sixth degree crystalline field parameters are each about 10 per cent smaller in the latter anion than in PrCl63-.

ISSN:0026-8976    

DOI:10.1080/00268978600100521

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

From the detailed assignment of the 15K excitation and absorption spectra, the energy level scheme given by previous authors is shown to be incorrect for the excited terms4I13/2,4I11/2,4F7/2and4F5/2of Er3+in Cs2NaErCl6. Additional data for the4I9/2term enable the first thirty excited states of Er3+to be located in this elpasolite lattice. The luminescence behaviour of Cs2NaErCl6is unusual in that a green-ultraviolet upconversion takes place, and that luminescence is expected but not observed from the4F5/2term. The excitation spectra are used to elucidate the mechanisms of these processes.

ISSN:0026-8976    

DOI:10.1080/00268978600100531

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The strong evidence that realistic pair potentials plus long-range many-body interactions provide an accurate quantitative description of the properties of gaseous and condensed rare gases is reviewed. The difficulties ofab initioquantal calculations of overlap-dependent many-body interactions are emphasized. It is shown that existing calculations are insufficient to justify the recently stated and repeated conclusion that the agreement with experiment found with such potentials is fortuitous.

ISSN:0026-8976    

DOI:10.1080/00268978600100541

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A semiclassical molecular dynamics method based on the approximate variational solution of the time-dependent Schrödinger equation with gaussian wave packets [1–3] has been applied to the simulation of liquid, solid and gaseous neon. The technique is computationally stable: the wave packets do not spread and the conservation of energy is excellent. With a suitable choice of the pair potential fairly satisfactory agreement with the experimental energy and pressure is obtained. The radial distribution functions exaggerate the quantum-mechanical broadening effect. Diffusion constants are in fair agreement with experiment and lower than those of the classical Lennard-Jones liquid.

ISSN:0026-8976    

DOI:10.1080/00268978600100551

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Potential energy surfaces obtained by combining semi-empirical andab initiofunctions are used in Monte Carlo calculations to predict thermodynamic, structural and spectroscopic properties of 0·87 M aqueous KCl, KF, LiF solutions. Intramolecular spectra are evalated using the frozen-field local-mode method of Reimers and Watts. The calculated properties are generally in good qualitative agreement with experimental observations and are interpreted in terms of the structure-making or structure-breaking effects of the ions. An analysis of the OH stretching band is given in terms of the local environments of the individual OH oscillators.

ISSN:0026-8976    

DOI:10.1080/00268978600100561

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A geometry for simulation of polar surfaces of ionic crystals is described. The simulation cells form a two-dimensional periodic array with one side bounded by the polar surface of a large piece of rigid ionic crystal. To simulate a polar surface in this way, the surface must carry excess charge to ensure that the cells are a model of the surface of a piece of crystal in bulk thermodynamic equilibrium. The electrostatic energy of the simulation cells is presented as a sum of convergent two dimensional lattice sums. The cancellation of divergences implicit in this energy because of the excess charge distributions is described in detail.

ISSN:0026-8976    

DOI:10.1080/00268978600100571

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The sensitivity of the results obtained within a recently proposed theory of freezing is tested againstallthe underlying approximations: (1) the Percus-Yevick approximation for the direct correlation function, (2) the choice of the effective fluid whose structure scales with that of the solid, (3) the path joining the solid to the fluid phase, and (4) the gaussian approximation for the local density of the solid. The general features of the freezing transition are stable with respect to the approximations while the quantitative agreement with the simulation results improves with the quality of the approximations. We also propose a semi-empirical hard-sphere direct correlation function which may be useful for other applications.

ISSN:0026-8976    

DOI:10.1080/00268978600100581

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor