摘要:

Accurate classical trajectory calculations have been carried out to assess the quality of two O2-He and two O2-Ne potential energy surfaces. The four potential energy surfaces have been obtained originally from the inversion of molecular beam scattering data and a limited selection of transport property data. In all four cases the transport property data were analysed using the infinite-order sudden approximation for the scattering dynamics, combined with first Chapman-Cowling approximation expressions for the transport coefficients. The present analyses employ considerably more accurate classical trajectory calculations for the scattering dynamics, together with Chapman-Cowling second approximation expressions for the transport coefficients. The higher level of approximation is clearly seen to be necessary at the present level of comparison. Moreover, the present analyses also examine a number of relaxation and field-effect phenomena (which are very much more sensitive to the anisotropic nature of the potential energy surfaces than are the ordinary transport phenomena), including pressure-broadening of the magnetic dipole-allowed and rotational Raman spectral lines of O2. For each interaction only one of the two potential surfaces examined is found to agree well with all the non-equilibrium phenomena presently examined. For the O2-He interaction the potential of Faubelet al.and for the O2-Ne interaction, the potential of Beneventiet al.provide the best overall agreement with available experimental data. It is clear that the measurement of additional relaxation and field-effect phenomena for O2-He, Ne mixtures would be most useful for further delineation between proposed potential energy surfaces for these interactions.

ISSN:0026-8976    

DOI:10.1080/00268979300100361

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In this paper we write down equations of motion (following the approach pioneered by Hoover) for an exact isothermal-isobaric molecular dynamics simulation, and we extend them to multiple thermostating rates, to a shape-varying cell and to molecular systems, coherently with the previous ‘extended system method’. An integration scheme is proposed together with a numerical illustration of the method.

ISSN:0026-8976    

DOI:10.1080/00268979300100371

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We report results of the vibrational analysis of monofluoroacetylene (HCCF) within the framework of the vibron model. We test the power (and limitations) of this model against the extensive database that has become available for this molecule. We are able to reach, with 14 parameters, a r.m.s. deviation of ≈ 5 cm-1over 103 bands.

ISSN:0026-8976    

DOI:10.1080/00268979300100381

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We report results of calculations of the rotational constants of HCCF recently measured by Holland, Newnham and Mills. We are able to reach, with five parameters, a r.m.s. deviation of ≈5 × 10-4cm-1over 76 bands. We also present a study of the Fermi resonances 2ν4- ν3, 2ν3- - ν2and 2ν2+ ν3- ν1, where we find results similar to those of Millset al.

ISSN:0026-8976    

DOI:10.1080/00268979300100391

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The high resolution infrared emission spectrum of barium monohydride was recorded. The fundamental and two hot band transitions were measured for the main isotopic species138BaH, and the fundamental band was measured for the minor isotopic species137BaH,136BaH, and135BaH. Improved Dunham constants were determined for all four isotopomers. The sensitivity of the infrared emission technique was demonstrated by the improved accuracy of the Dunham constants.

ISSN:0026-8976    

DOI:10.1080/00268979300100401

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We review the existing simulation data and equations of state for the Lennard-Jones (LJ) fluid, and present new simulation results for both the cut and shifted and the full LJ potential. New parameters for the modified Benedict-Webb-Rubin (MBWR) equation of state used by Nicolas, Gubbins, Streett and Tildesley are presented. In contrast to previous equations, the new equation is accurate for calculations of vapour-liquid equilibria. The equation also accurately correlates pressures and internal energies from the triple point to about 4·5 times the critical temperature over the entire fluid range. An equation of state for the cut and shifted LJ fluid is presented and compared with the simulation data of this work, and previously published Gibbs ensemble data. The MBWR equation of state can be extended to mixtures via the van der Waals one-fluid theory mixing rules. Calculations for binary fluid mixtures are found to be accurate when compared with Gibbs ensemble simulations.

ISSN:0026-8976    

DOI:10.1080/00268979300100411

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A new Monte Carlo dynamics algorithm for simulating the motions of hydrocarbon chains is presented. The algorithm utilizes the high coordination {2 1 0} lattice for the simultaneous representation of polymethylene and unsaturated chains. While the dynamics of saturated chains may be described as the superposition of local conformational changes, the motion of the planar unsaturated segments can be simulated only through the introduction of cooperative moves. Simulations of the motions in isolated 18-carbon chains show that the introduction of acisdouble bond increases the relaxation rates for torsional motions, while the introduction of atransdouble bond has the opposite effect. The difference in behaviour appears to arise simply from geometrical constraints.

ISSN:0026-8976    

DOI:10.1080/00268979300100421

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A general treatment of spin dynamics during coherence transfer is presented as an example of a many-body problem under strong coupling. In a previous paper, coherence transfer by isotropic mixing (IM) between two coupled spins was examined. However, the greatest experimental interest in the technique of IM centers on the transfer of coherence between spins that are not directly coupled. The dynamics of coherence transfer in multiple spin systems are cast in a superoperator formulation, in which diagonalization of the mixing Liouvilian matrix allows derivation of the coherence transfer frequencies from the eigenvalues. Development of a particular basis of the spin density operator space facilitates diagonalization of the strong coupling Liouvillian. This basis is completely reduced with respect to rotation, permutation, and particle number. Treatment of the many-body aspect is based on an approach using the Young tableaux. The exact calculation of the dynamics of coherence transfer in a three spin system is accomplished using the tableaux method, and closed form solutions are compared with results obtained using numerical methods. The degree to which practical coherence transfer pulse sequences deviate from ideal isotropic mixing, and the effect that these deviations have on symmetry-induced selection rules is calculated numerically.

ISSN:0026-8976    

DOI:10.1080/00268979300100431

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Semi-empirical interaction potentials are used to determine the stable site and the adsorption energy of diatomic (CO) or symmetric top (CH3F) molecules physisorbed on NaCl(100) surface. Within the approximation of harmonic molecular motions and rigid NaCl substrate, the adsorption energy is calculated and compared to experimental values deduced from thermodynamic measurements. The contribution of the electric interaction between the polar molecules and the ionic substrate is dominant since it represents 75% of the total energy.

ISSN:0026-8976    

DOI:10.1080/00268979300100441

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The order matrices for 19 dihalobenzenes of Csand C2vsymmetry have been measured using the NMR spectra of these molecules as solutes in the nematic mixture of 55 wt% Merck ZLI-1132 and 45 wt%N-(4-ethoxybenzylidene)-2,6-dideutero-4′-n-butylaniline. In this liquid crystal, the contribution to the orientational potential from the interaction between the molecular quadrupole moment and the mean electric field gradient of the liquid crystal can be neglected. The results are compared with predictions of a model which describes the anisotropic intermolecular potential in terms of (1) an elastic distortion of the liquid crystal and (2) an anisotropic surface interaction between solute and liquid crystal. Not only are the largest (in magnitude) order parameters very well fitted, but also the calculated anisotropies in the order matrices agree with the experimental ones. It is demonstrated that the results cannot be fitted with a bond-additive approach.

ISSN:0026-8976    

DOI:10.1080/00268979300100451

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor