摘要:

An intermolecular pair potential energy function has been developed for nitrogen which is able to reconcile theoretical results for the system with experimental data for various bulk properties. The long and short range forms of the potential are known from quantum mechanical calculations. Modifications to the quadrupole-quadrupole energy due to electron charge overlap effects have been included. In the well region, many different representations have been studied and have been assessed by fitting to experimental data, chiefly for the low temperature lattice properties and second virial coefficients. A number of functions have been derived which are able to reproduce the available information within experimental error. Corrections for non-additive three body terms have been included in calculating the lattice properties, and the first order quantum corrections to the virial coefficients were also included. The dilute gas shear viscosity (based on the Monchick-Mason approximation) was also calculated and used to discriminate between different possible potential energy functions. Other properties such as the isothermal comressibility of α-N2at 0 K and the α-γ phase transition at high pressure were also studied and provided further tests of the best potential. The minimum energy dimer configuration was also investigated. We have also tried to represent our model potential analytically in the form of an expansion using spherical harmonics.

ISSN:0026-8976    

DOI:10.1080/00268978400100571

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Lines in the fundamental band of the SiH radical in its ground2Π state have been observed by laser magnetic resonance spectroscopy at 5 μm. The measurements are used to determine values for the relevant molecular parameters for28SiH.

ISSN:0026-8976    

DOI:10.1080/00268978400100581

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Variationally exact rovibrational levels for the H3+and H2D+molecules are calculated using a recently published accurate potential. Vibrational fundamentals arevA1= 3191 cm-1andvE= 2494 (2521·6) cm-1for H3+andv1= 3000 cm-1,v2= 2184 cm-1andv3= 2310 cm-1for H2D+. For H3+calculated ground state rotational constants areB0= 43·51 (43·57) cm-1,C0= 20·59 (20·71) cm-1,DJ0= 0·04 (0·05) cm-1,DJ K0= -0·07 (-0·10) cm-1andDK= 0·04 (0·04) cm-1(where experimental results are given in parenthesis). An attempt is made to stabilize many vibrational states. We thus reassess the results of Carney and Porter. The implications for astrophysics, the interpretation of the infrared spectrum of H3+near its dissociation limit and the unassigned spectrum of H2D+are discussed.

ISSN:0026-8976    

DOI:10.1080/00268978400100591

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The general form of the corrections to the vibration-rotation hamiltonian resulting from isotope substitution of heavy nuclei has been obtained. These results are used for predicting the displacements of the vibration-rotation line centres. Some results of numerical calculations are given as an illustration.

ISSN:0026-8976    

DOI:10.1080/00268978400100601

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The rotational diffusion of rod-like macromolecules, idealized as monodisperse rods, in concentrated solution is considered. The Doi-Edwards model is modified to explain the experimentally observed increase of the rotational relaxation time with increasing concentration in the lyotropic-nematic phase of rigid rod-like molecules in solution. Our approach consists in (i) reconsidering the original Doi-Edwards model to eliminate unphysical behaviour of the rotational relaxation time at the limit of perfect order, and (ii) including concentration effects on the translational diffusivity of rods in the Doi-Edwards model. Predictions of the corrected model are compared with steady flow viscosity data for poly(n-alkylisocyanates). In the lyotropic-nematic phase a very good qualitative agreement between the theory and experiment is observed. Additionally, the model applied to a highly concentrated isotropic phase explains in a natural way the viscosity behaviour as the concentration is increased towards the critical value for formation of the lyotropic-nematic phase.

ISSN:0026-8976    

DOI:10.1080/00268978400100611

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The E.P.R. spectra of the lowest triplet state of each of 1,3- and 1,7-diazanaphthalene in solid solution in durene single crystals at 97 K are reported. They reveal deviations from perfect guest substitution. Detailed crystal packing calculations using atom-atom potentials and allowing for host lattice relaxation confirm that guest rotations about the normal axis are to be expected and could be several tens of degrees away from perfect substitution. Furthermore, guest centre of mass positions can be up to 1 Å away from the inversion centre of durene. The calculated potential curves with respect to this rotation show shallow potential minima corresponding to metastable sites but there is a considerable sensitivity to the potential set used. The broad, shallow features of the potential wells suggest that measurements at liquid nitrogen temperatures, representing an orientation which is time-averaged over several quanta of the lowest frequency librational mode, may well differ from those recorded at liquid helium temperatures.

ISSN:0026-8976    

DOI:10.1080/00268978400100621

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

We report Monte Carlo (MC) simulation results for pure and mixed fluids of hard homonuclear diatomic molecules (dumbells) with added point charges arranged in a quadrupolar symmetry; for completeness we include the case of hard spheres with added point charge quadrupoles. We calculate the thermodynamic and structural properties. Included in the calculations are mixtures in which the two components have quadrupoles of opposite signs, as well as quadrupolar/non-polar mixtures; the molecules can have the same or differing core shapes. The point charges lead to a pronounced preference for molecular pairs to adopt ‘T’ configurations in the pure fluids; this is also true for the like pairsAAandBBin the mixtures. In mixtures of two quadrupoles of opposite sign the unlike pairABstructure is strikingly different from theAAandBBstructures, because of the strong preference forABpairs to adopt parallel or end-to-end configurations. Changing the shape of the molecular core from a sphere to a dumbell interferes with the ability of the molecules to adopt those configurations favoured by the quadrupoles, and leads generally to larger configurational energies and pressures.

ISSN:0026-8976    

DOI:10.1080/00268978400100631

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Contrast variation neutron small angle scattering experiments have been used to determine the configuration of the polar head groups in cationic micelles of tetradecyl trimethyl ammonium bromide in which either the paraffin chain or trimethyl ammonium polar head had been selectively deuterated.

ISSN:0026-8976    

DOI:10.1080/00268978400100641

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The statistical mechanics of inhomogeneous systems is usefully discussed from at least two complementary approaches: (i) the virial route, in which calculations of the structure and the thermodynamic properties are based on knowledge of the intermolecular forces in conjunction with the distribution function hierarchy, and (ii) the fluctuation theory route, based on formal results linking the equilibrium structure and properties of a system to its response to a change in external field. This paper makes use of both of these approaches to discuss the properties of a fluid in the presence of a strong localized external field. Particular attention is paid to the limiting case when the external field acts as a hard wall. Fluctuation theory yields a unified approach to interfaces stabilized by one body external fields of arbitrary strength, the strength determining the stability of the interfacial boundary with respect to wave-like fluctuations; with the weak field limit identified as a free fluid-fluid interface.

ISSN:0026-8976    

DOI:10.1080/00268978400100651

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Simulations generating a statistical ensemble of configurations of a molecular system provide information to derive entropy. For cases where the spatial distribution is bounded, the entropy can be derived from the average of the logarithm of the spatial probability density, but will be subject to systematic errors due to statistical fluctuations. A method is given to eliminate these errors by using different interval sizes and fitting the results to a simple theoretical expression. The method is feasible when the multidimensional case can be broken up into a sum of low dimensional contributions. The validity of the latter approximation and ways to correct for correlations are discussed.

ISSN:0026-8976    

DOI:10.1080/00268978400100661

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor