摘要:

The three lowest fundamental bandsv9,v6andv5of D2CCO have been studied at a resolution ofca.0·003 cm-1from infrared spectra obtained at room temperature. A set of high quality ground state rotational and centrifugal distortion constants has been obtained. From an analysis of infrared ground state combination differences together with the microwave and millimeterwave measurements of Nemes and Winnewisser [6] we obtained the following rotational ground state constants:

ISSN:0026-8976    

DOI:10.1080/00268978700101131

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The free energy of a classical system of particles interacting with a square-well potential is calculated as a function of the width of the well. An expansion around a reference system of definite range is made, and the range difference is treated as a small parameter. The short-range case is obtained when a hardsphere system is used as reference. This expansion is carried out to third order in the width of the well, and leads to closed-form expressions which are analytic in the range and the thermodynamic variables, except for two quadratures. These can be resolved by the use of the superposition approximation or the Percus-Yevick theory. Results are obtained for the first two terms of the free energy in a high temperature expansion and are compared with Monte Carlo data. The method gives very good results for short range and most of the fluid range.

ISSN:0026-8976    

DOI:10.1080/00268978700101141

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

We present a simple model to deal with long range electrostatic interactions in computer simulations of solvated molecules and ions. The model combines a discrete molecular description of the first two or three solvation layers with a continuum description of the bulk solvent. The solute is described quantum mechanically. For a series of amines good agreement with experimental protonation energies in water is obtained, when the position of the continuum boundary takes properly into account the volume of the enclosed particles. A comparison is made with periodic boundary simulations and with existing continuum models. The accuracy depends not only on the dielectric model itself, but at least as much on details of the electrostatic potential and on inductive interactions.

ISSN:0026-8976    

DOI:10.1080/00268978700101151

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Thev1fundamental band of HOCS+has been observed in absorption in a hollow cathode discharge with a difference frequency laser system. The precise spectroscopic parameters have been determined through a least squares fit of more than 550 lines to an effective vibration-rotation hamiltonian. It has been concluded that the species is HOCS+, since the vibrational frequency (v0= 3435·1636 cm-1) is very likely to be the O-H stretch, and not an S-H or C-H stretch. Rotational transition frequencies forKa⩽ 2 are calculated to assist the search for the species in interstellar space and in the laboratory. An isomer, HSCO+, has been searched for in the range of 2450–2600 cm-1(expected S-H stretch frequency region) without success.

ISSN:0026-8976    

DOI:10.1080/00268978700101161

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A statistical mechanical perturbation theory due to Fischer has been used to calculate thermodynamic properties of liquid nitrogen for model intermolecular potentials due to Cheung and Powles (CP), Raich and Gillis (RG), and Berns and van der Avoird (BV). Refinements in the numerical implementation of the Fischer theory are described. Results for the CP potential agree well with both simulation and experimental data except at high density and high temperature. Differences between theory and experiment are usually comparable to the differences between two sets of experimental data for the CP potential but are generally larger for the other two potentials. For both BV and RG potentials the excess Helmholtz energies and excess internal energies are up to 15 and 10 per cent higher, respectively, than experimental values whereas the predicted pressures are low by 100–200 bar for RG and 50–100 bar for BV. The BV potential is slightly more satisfactory than the RG potential overall. Results for spherical harmonic components of the radial correlation function for the CP potential calculated using zeroth and first order approximations in the Fischer theory and also in the RAM theory are also compared with results from molecular dynamics simulations.

ISSN:0026-8976    

DOI:10.1080/00268978700101171

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Several vibrational bands of theB1-X1Σ+electronic transition of PbS were observed using laser excitation spectroscopy on a collimated molecular beam. For theB1 state highly accurate molecular constants were derived and a small Ω doubling was analysed. Isotopic field shift parameters are compared to those of theA0+-X1Σ+transition. The hyperfine splitting observed for207Pb32S depends on the parity of the levels and is interpreted in terms of Ω hyperfine doubling.

ISSN:0026-8976    

DOI:10.1080/00268978700101181

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Essentially exact calculations of the transport collision integrals for a realistic model of the intermolecular pair potential of helium and nitrogen are reported. The collision dynamics for the interaction of the atom and molecule have been treated within the framework of the Arthurs and Dalgarno closecoupled formalism and the calculations are free from all approximation except inevitable numerical round-off. The direct calculation of collision integrals covers the temperature range 70 K to 300 K. The range has been extended upwards to 500 K with the aid of complementary classical calculations without loss of accuracy.

ISSN:0026-8976    

DOI:10.1080/00268978700101191

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The absorption spectra of UCl2-6diluted into the cubic lattices Cs2ZrCl6and Cs2SnCl6, and of UBr2-6diluted into Cs2ZrBr6have been measured at liquid helium temperatures. The derived energy levels, together with earlier luminescence measurements have been used to evaluate the crystal-field, spinorbit coupling, inter-electron repulsion and Trees correction parameters and the corresponding eigenvalues. Several of the states are derived from an almost equal admixture of two or more Russell-Saunders terms. Some magnetic properties are also computed and discussed.

ISSN:0026-8976    

DOI:10.1080/00268978700101201

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The conformational states of linear hydrocarbons as a function of internal energy are enumerated. The principal nonbonded interaction, the pentane effect, is assigned a finite energy, but other nonbonded interactions are neglected. Using a generating function technique several equivalent expressions are derived forN(n,ng,np), the number of conformations of a chain withnrotatable bonds,nggauche bonds andnpadjacent opposite rotations. A combinatorial interpretation for these expressions is given and the asymptotic behaviour is studied. A similar analysis is made forT(n,np), the total number of states with a fixed number of pairs, but no restriction onng. These results clarify and extend other recent work. A general framework for including other nonbonded interactions is constructed and illustrated. Finally it is shown that a relation between the generating function and the partition function gives an exact expression for the latter.

ISSN:0026-8976    

DOI:10.1080/00268978700101211

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

We get a solution of the Bhatnagar-Gross-Krook (BGK) model kinetic equation by means of a perturbative expansion of a temperature gradient to study the transport properties in a gas with large shear rate. The irreversible fluxes are evaluated exactly to first order in the expansion for Maxwell molecules. The transport coefficients obtained are highly nonlinear functions of the shear rate. This dependence on shear rate is analysed and compared with previous results for several transport coefficients. Finally, we have found a solution for a simple model of constant collision frequency for which a large shear rate coexists with an arbitrary temperature gradient.

ISSN:0026-8976    

DOI:10.1080/00268978700101221

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor