摘要:

A quantum-dynamical method is described for investigating the translational-vibrational energy transfer that occurs in the collinear collision of an atom with a linear triatomic molecule. The technique is applied to the computation of vibrational transition probabilities for the collinear collisions of helium atoms with CO2, OCS and HCN over a range of energies. Realistic potentials are used for the triatomic molecules while simple exponential or Morse potentials are used to describe the helium-molecule interaction. The effects of varying the atomic masses and the potential function parameters are examined. It is found, that the symmetric stretch vibrational modes of CO2, OCS and HCN are preferentially excited (or relaxed), by collision with the atom, over the asymmetric stretch modes.

ISSN:0026-8976    

DOI:10.1080/00268978000101091

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Perturbation theory results are obtained for the case of the two centre Lennard-Jones fluid by using a spherically averaged reference fluid. It is shown that the perturbation theory, although roughly correct, does not provide a quantitative description of the molecular structure.

ISSN:0026-8976    

DOI:10.1080/00268978000101101

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The fully relativistic Dirac-Fock generalizations of non-relativistic Phillips-Kleinman and generalized Phillips-Kleinman pseudopotentials are used to derive pseudopotential theories based on the Schrödinger hamiltonian which incorporate relativistic effects.

ISSN:0026-8976    

DOI:10.1080/00268978000101111

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

We have measured simultaneously the thermal resistivity and the heat capacity per unit volume for phases I, II, III and IV of CBr4. We have used the transient hot-wire method, and have made measurements over the ranges 170 K to 425 K, and up to 2 GPa. Our results, and other evidence, indicate that I and III are plastic crystal phases, and that there is a significant degree of structural disorder in phase II. Three-phonon interactions probably provide the dominant contribution to the thermal resistivity of phase IV. Using structural analogies with the phases of CCl4, we find that the relative values of the thermal resistivities are roughly as predicted by simple theory.

ISSN:0026-8976    

DOI:10.1080/00268978000101121

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The dynamics of molecular rototranslation are treated with an equation of motion with a non-Markovian, stochastic force/torque. It is shown that this Mori/Kubo/Zwanzig representation is equivalent to a multidimensional Markov equation which may be identified with analytical models of the molecular motion. Langevin and Fokker-Planck equations for two such models are derived from the general equations of motion. The analytical results are compared with a computer simulation of the velocity/angular velocity mixed autocorrelation function,Cvω(t) = <v(0) . ω(t)> for a triatomic ofC2vsymmetry.

ISSN:0026-8976    

DOI:10.1080/00268978000101131

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A multidimensional expansion of the Mori equation in terms of a chain of Markov equations is used to develop a theory of molecular rototranslation in condensed phases. The stochastic equations of motion are solved for transient and equilibrium averages of the relevant dynamical variables. The single particle rototranslational Langevin equations correspond to the first equation of the Markov chain and (with a rotational constraint) are solved using Wiener matrix algebra for a possible sixteen autocorrelation functions. The Einstein result for the mean-square velocity and angular velocity is generalized. The third dimension of the Markov chain corresponds mechanically to the (constrained) rototranslation of a molecule bound to a cage of nearest neighbours by a dissipative matrix γ. The cage is itself undergoing a rototranslational Brownian motion. The problem of evaluating the formal theory with experimental measurements is discussed in terms of the number of parameters associated with each approximant (or dimensionality of the Markov chain). It is possible to avoid using a least-mean-squares fitting procedure by using a broad enough range of data and simulator results.

ISSN:0026-8976    

DOI:10.1080/00268978000101141

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Symmetry constraints on coefficients in the generalized spherical harmonic expansions of configurational properties are derived for pairs of non-linear molecules. Constraints are also obtained for the coefficients in the expansion of the time dependent reorientational distribution function for a non-linear molecule. In addition to invariance under the operations of the molecular point group, these properties must be invariant to interchange (for pairs of identical molecules) and to changes in the ‘handedness’ of the coordinate axes (for optically inactive molecules). Specific results are given for the configurational properties of tetrahedra, but other simple non-linear point groups are briefly considered. In the time dependent case, several types of molecular symmetry are discussed (including tetrahedral), and the relationship between point group constraints and the results for anisotropic rotational diffusion models is clarified.

ISSN:0026-8976    

DOI:10.1080/00268978000101151

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Proton distance ratios and elements of the order tensor are obtained from nuclear magnetic resonance spectra of chloro-, bromo-, and iodobenzene partially oriented in a potassium laurate lyotropic mesophase. Corrections for harmonic vibrations are applied and it is shown that even for proton distance ratios these corrections are significant. Furthermore, the effects of solvent on the ratios determined are comparable to the effect of the substituent. Particular attention to weighting of the dipolar coupling in the structural analysis is necessary if values are to be judged significant to 1 part in 104. The elements of the order tensor are discussed in terms of the orienting influence of the interface and alkyl chains of the mesophase surfactant.

ISSN:0026-8976    

DOI:10.1080/00268978000101161

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

From the derivative of the statistical mechanical definition of the number density (the first Yvon equation), we derive an infinite set of sum rules that must be satisfied by the density profile and the pair correlation function of a liquid-vapour system with pairwise central interactions. For a particular class of approximate pair correlation functions, the sum rules reduce to equations linking the pressure and temperature with the densities of the two bulk phases. Good agreement with experimental data is obtained.

ISSN:0026-8976    

DOI:10.1080/00268978000101171

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A new integral equation for describing multicomponent classical molecular fluids at equilibrium is presented; the derivation of this theory makes use of the functional Taylor expansion technique of Percus and the Fourier-Wigner expansion. A diagrammatic analysis of the equation is developed and the theory is discussed.

ISSN:0026-8976    

DOI:10.1080/00268978000101181

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor