摘要:

Ab initioself-consistent field calculations of the electric field gradients (efg) at the nuclei in hydrogen bonded pentamers of H2O are reported, and the shifts relative to the isolated molecule discussed with reference to the importance of the electrostatic, polarization, exchange and charge transfer mechanisms. The results of electrostatic model calculations on ice structures in which a single H2O molecule as well as a hydrogen bonded pentamer (treated quantum mechanically) are surrounded by a point charge representation of the remaining molecules in the crystal lattice are also presented. The calculated efg shifts are compared with the observed solid state shifts in the nuclear quadrupole coupling constants for normal ice (Ih) and the high pressure polymorph ice VIII, assuming that the17O and2H nuclear quadrupole moments are -2·63 fm2and 0·286 fm2respectively. A new estimate of the17O nuclear quadrupole coupling constant in liquid water is also proposed; this is χ(17O) = 8·5 ± 0·5 MHz.

ISSN:0026-8976    

DOI:10.1080/00268978700101481

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A methodology is presented for Monte Carlo simulation of fluids in a new ensemble that can be used to obtain phase coexistence properties of multicomponent systems from a single computer experiment. The method is based on performing a simulation simultaneously in two distinct physical regions of generally different densities and compositions. Three types of perturbations are performed, a random displacement of molecules that ensures equilibrium within each region, an equal and opposite change in the volume of the two regions that results in equality of pressures, and random transfers of molecules that equalize the chemical potentials of each component in the two regions. The method is applied to the calculation of the liquid-gas coexistence envelope for the pure Lennard-Jones (6, 12) fluid for several reduced temperatures from the vicinity of the triple point to close to the critical point (T* = 0·75 toT* = 1·30). Good overall agreement with previously available literature results is obtained, with some deviations at the extremes of this temperature range.

ISSN:0026-8976    

DOI:10.1080/00268978700101491

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Translational photofragment spectroscopy has been used to study the photodissociation dynamics of n-C3H7I and i-C3H7I at 248 nm. The measured anisotropies of the photofragments show that the initial absorption is the (parallel polarized)3Q0←Ntransition with a dissociation lifetimes of 3·7 ± 2 × 10-13s and 2·5 ± 2 × 10-13s respectively. The of flight measurements yield the energy disposal for channels leading to I(2P3/2) and I*(2P1/2) for both molecules, although with greater uncertainty for i-C3H7I. The average energy disposed into translation is 43 per cent (I) and 52 per cent (I*) for n-C3H7I, and 39 per cent (I) and 57 per cent (I*) for i-C3H7I.

ISSN:0026-8976    

DOI:10.1080/00268978700101501

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A simple fitting formula for the correlation functions and the static structure factor of inverse-power fluids is given in terms of the known solution of the mean spherical approximation for Yukawa interaction. The only input is the equation of state. Comparison with computer simulation and accurate integral equations shows very good agreement.

ISSN:0026-8976    

DOI:10.1080/00268978700101511

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Reactive scattering of F atoms with ICl molecules has been studied at an initial translational energyE∼ 34 kJ mol-1, using a supersonic beam of F atoms seeded in He buffer gas. Laboratory angular and velocity distributions of IF product have been measured which show scattering peaking sharply in the forward direction with a smaller backward peak of relative height ∼0·5 ± 0·1. The product translational energy for scattering in the forward direction is greater than that for the sideways and backward scattering. Thus direct stripping dynamics contribute to the forward scattering, while the reaction dynamics are otherwise characterized by a short-lived complex mechanism. Bent structures are proposed for the collision complex and the reactant transition state. The observed scattering is related to the initial orientation of the reactant ICl molecule with respect to the incident F atom direction, by the precessional motion of an asymmetric top intermediate which is perturbed by vibrational-rotational energy transfer and becomes unstable for motion far removed from the plane of collision.

ISSN:0026-8976    

DOI:10.1080/00268978700101521

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Differential reaction cross sections have been calculated from the classical precessional motion of a bent triatomic long-lived complex which constitutes an asymmetric top. The angular distributions are similar to those predicted by the Halpern Strutinski model for precession of a symmetric top but the singularities of this model are rounded off and the abrupt fall to zero is replaced by a smooth decline. Consideration of the stability of asymmetric top precession suggests that vibrational-rotational energy exchange may separate the motion of short-lived complexes rotating close to the plane of collision from the motion of those rotating far from the plane of collision.

ISSN:0026-8976    

DOI:10.1080/00268978700101531

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

We report the finite fractal analysis of trajectories of finite elapsed time for the molecules in realistic liquids and for some model fluids, by Richardson's method. The properties are much richer for finite than for infinite trajectories. An adequate explanation of the scaling properties at scale larger than the r.m.s. end to end length of the trajectory is given by the ‘diffusion approximation’. It is shown that this analysis of finite trajectories is of prime importance in any attempt to resolve the present controversy regarding the behaviour of real trajectories at large scale, in particular. It is shown that if in the analysis of trajectories one averages over a number of trajectories then the method of averaging commonly used is incorrect and the correct procedure is given.

ISSN:0026-8976    

DOI:10.1080/00268978700101541

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Symmetry breaking corrections for HD+are estimated by performing a unitary transformation on the hamiltonian. The terms responsible forg/ucoupling are removed from the kinetic energy operator at the expense of introducing additional terms in the potential. The effective electrostatic potential may be interpreted in terms of effective nuclear charges. A new hamiltonian having the correct dissociation limits is obtained and the corresponding Schrödinger equation is largely separable. The resulting corrections to the energy compare well with previous work, particularly at large bond lengths, and the electric dipole moment and electron densities at the nuclei show the correct behaviour near dissociation.

ISSN:0026-8976    

DOI:10.1080/00268978700101551

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The quantum corrections to the thermodynamic properties of molecular fluid mixtures are calculated. We have taken into account the influence of quadrupole moment, induced dipole moment, anisotropic dispersion and shape factor. The theory is applied to equimolar binary mixtures and numerical results are reported for N2-O2, N2-Ar and O2-Ar at zero pressure. Agreement with experiment for the excess molar properties such as excess molar volume, excess Gibb's free energy and excess enthalpy of these systems is found to be fairly good.

ISSN:0026-8976    

DOI:10.1080/00268978700101561

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The structure factor for a two component mixture of dilute charged colloidal suspensions is measured for different compositions using polarized light scattering. A rescaled mean spherical approximation method for calculating the structure factor for the mixture under the substitutional model is given. The measured structure factor agrees very well with the calculated one. The reason for the adequacy of the substitutional model for the colloidal mixture is discussed.

ISSN:0026-8976    

DOI:10.1080/00268978700101571

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor