摘要:

Molecular dynamics simulations of a model of CS2have been analysed to calculate the shapes and intensities of the Rayleigh and allowed Raman bands of the liquid. The calculations are performed using the first order dipole induced dipole mechanism (DID). There is a clear time scale separation between the collision induced and reorientational components of the spectrum which becomes more marked at lower temperatures. The projection factors which determine the effective polarizabilities are large for CS2at first order DID and second order DID terms calculated for the Raman polarizabilities are also substantial. An empirical renormalization scheme to incorporate higher order DID effects for the Raman intensities is described. A simple model which neglects orientational correlations and orientational translational correlations provides a semi quantitative prediction of the collision induced intensities.

ISSN:0026-8976    

DOI:10.1080/00268978500101831

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The molecular dynamics technique has been used to simulate patches of solid nitrogen adsorbed on the basal plane of graphite. A model of the molecule-surface interaction involving an isotropic site-site interaction predicts a melting transition 9 K below the experimentally observed temperature and leads to an adsorbed liquid patch on melting. By including the anisotropy in the site-site interaction the lateral surface barriers are increased and a site-site potential of the form

ISSN:0026-8976    

DOI:10.1080/00268978500101841

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The multipole formulation of N.M.R. is applied to small spin systems interacting via scalar coupling. Two scalar coupled spins of 1/2 are treated in detail for bases that are irreducible under the rotation group, SO(3). Particular attention is focused on the role of the bilinear operators in providing a pathway for coupling. A complete analytical solution for the two spin-1/2 problem is given.

ISSN:0026-8976    

DOI:10.1080/00268978500101851

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Using a two-spin multipole formulation, spin decoupling is analysed analytically from arbitrary initial spin preparations. The rotating frame which is most convenient is ω ≡ 1/2(ω01+ ω02) rather than the commonly used Larmor frequency of the irradiated spin ω02. The importance of unobserved polarizations (bilinear operators) is stressed by identifying these terms as providing pathways to spin coupling which must be destroyed for decoupling. Appropriate linear combinations of the bilinear polarizations can be rotated by the perturbing field. Some general observations of the effects of periodic pulse sequences and amplitude modulation are included.

ISSN:0026-8976    

DOI:10.1080/00268978500101861

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The multipole formulation of N.M.R., as applied to multi-spin systems, makes use of a basis that is composed of rotationally invariant tensor operators. For spin systems that have magnetic symmetry, it is possible to adapt this Liouville space into a basis which is also irreducible under the appropriate permutation symmetry. This permits a systematic treatment of the various multiquantum spectra and leads to a dramatic factorization of the Liouville matrix. Examples ofAA′ andAA′BB′ ≡ [AB]2systems are included as illustrations. The effect of introducing the weak coupling limit is shown to further reduce the dimensionality of submatrices for the related [AX]2system.

ISSN:0026-8976    

DOI:10.1080/00268978500101871

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Simulations by Langevin dynamics technique are compared with molecular dynamics simulations. The potential of mean force and the self-diffusion coefficients at infinite dilution are obtained from suitable molecular dynamics simulations. A very simple case is studied: pure liquid krypton at three different thermodynamic states. Radial distribution functions obtained by both methods are in good agreement but marked discrepancies in time correlation functions and in self-diffusion coefficients are observed. These discrepancies may be attributed to hydrodynamic interactions and memory effects, which are ignored in our Langevin dynamics simulations.

ISSN:0026-8976    

DOI:10.1080/00268978500101881

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

We present a simple theory of the far-infrared collision-induced absorption spectrum of liquid methane. We assume that CIA arises through octopolar and hexadecapolar induction. By neglecting the small anisotropy in the intermolecular potential, we can represent the spectral profile as convolutions of single-molecule free rotation spectra with intermolecular translational components. Information theory is used to estimate the ‘ least biased ’ form for the latter, based on our knowledge of their zeroth and second spectral moments (the calculation of these moments is described in an appendix). In this way we avoid the need to make questionable assumptions about the system dynamics. Our theory contains no adjustable parameters, yet the computed lineshapes are in excellent agreement with the available experimental data.

ISSN:0026-8976    

DOI:10.1080/00268978500101891

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

We present a simple theory of the far-infrared collision-induced absorption spectrum of dilute solutions of methane in liquid argon. We assume that CIA arises through octopolar and hexadecapolar induction of a dipole on the solvent argon atoms by the solute methane molecules. By neglecting the small anisotropy in the CH4-Ar intermolecular potential, we can express the spectral profile as convolutions of CH4free rotation spectra with intermolecular CH4-Ar translational components. Information theory is used to estimate the ‘ least biased ’ form for the latter, based on our knowledge of their zeroth and second spectral moments. In this way we avoid the need to make questionable assumptions about the system dynamics. Our theory contains no adjustable parameters, yet yields results in excellent agreement with experiment.

ISSN:0026-8976    

DOI:10.1080/00268978500101901

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A study at SCF-CI level has been performed on the water dimer, with a [541|31] basis set. The effects of the correlation energy, basis set superposition error (BSSE) and Davidson correction were investigated. Maintaining the experimental water geometry, several sections of the energy surface were calculated. They show only one minimum energy structure, the linear trans dimer, in agreement with experiment. The linear cis and bifurcated forms are found to be unstable.

ISSN:0026-8976    

DOI:10.1080/00268978500101911

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Bond lengths and vibrational frequencies for Xe2+and Au2were computed using non-relativistic valence-electron wavefunctions with relativistic effective potentials and also using relativistic valence-electron wavefunctions with non-relativistic effective potentials. For both molecules the former gives the relativistic bond length and the latter and non-relativistic bond length. This appears to support the points of view that the relativistic bond length contraction is largely independent of atomic orbital contractions.

ISSN:0026-8976    

DOI:10.1080/00268978500101921

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor