摘要:

Neutron diffraction measurements of the structure factor of supercooled liquid D-glycerol are reported for the range 0·03 ≲Qˇ- 4·0Å-1at temperatures between 300 and 175 K. We find that the structure is essentially unchanged over this entire range. We expected some evidence of increased hydrogen bonding at the lower temperatures, but no direct evidence for any strong orientated density-density correlation at low-Qdue to a hydrogen bond is observed. To provide a contrast, the structure factor of vanadium pentafluoride is discussed briefly because vanadium pentafluoride is known to form fluorine-fluorine bridges in the dense state. We equate loosely this bridging with a hydrogen bond. In that compound there is evidence for F-F bridging at low-Q. Small angle Placzek corrections to the D-glycerol scattering cross section data are estimated.

ISSN:0026-8976    

DOI:10.1080/00268978700102871

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Residual specific heatscv/*are calculated from a Weeks-Chandler-Andersen-type perturbation theory for Lennard-Jones (LJ) and two-centre-Lennard-Jones (2CLJ) liquids. For spherical molecules the theory predicts that as the density is increased up to slightly above three times the critical density (ρc),cv/*increases to 2R. Corresponding states considerations indicate that rotational degrees of freedom in 2CLJ fluids make no contributions tocv/*. Comparing with real liquids, the theoretical predictions ofcv/*agree, within the accuracy of the experiments, with experimental data for liquid argon, methane, and oxygen, at densities ρ/ρc> 2·5. For ethane, the theoretical predictions ofcv/*, assuming a 2CLJ fluid with elongationL= 0·67, are too low. This deficiency in the theory for long molecules is attributed to the neglect of the angle-dependence of the background correlation function. However, computer simulation results forcv/*in 2CLJ fluids of elongationL= 0·67 agree with the perturbation theory predictions for the spherical LJ liquid at corresponding states. Again, for ρ/ρc> 2·5, both these latter results agree with the experimental values for ethane, within or nearly within the experimental accuracy.

ISSN:0026-8976    

DOI:10.1080/00268978700102881

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The carbon-13 isotropic chemical shifts and anisotropies of the shielding tensors of methyl halides (CH3F, CD3Br, CH3I) and haloforms (CHF3, CDCl3, CDBr3, CHI3) have been determined from carbon N.M.R. spectra in mixtures of liquid crystals with opposite anisotropy of diamagnetic susceptibility. By using these results the components of the chemical shielding tensors were determined. The tensor element σzz(zaxis parallel to theC3symmetry axis) was found to be approximately constant (ca.200 ppm) for methyl halides. The element σxx(= σyy) takes values between 84 ppm (for CH3F) and 226 ppm (for CH3I). On the contrary, the change of σzzfor haloforms was about three times larger than the change of σxx. The experimental shielding tensors of methyl halides have been compared with the theoretical ones calculated by the Coupled Hartree-Fock method. There is a good agreement between the experimental and theoretical values for σzz, but not for σxx. The difference of these values increases when the electronegativity of the substituent decreases, i.e. from F to I.

ISSN:0026-8976    

DOI:10.1080/00268978700102891

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

An analysis of the structured continuum fluorescence (280–390 nm), arising from excitation of IBr at 180 nm, 193 nm and 200 nm, is reported. The fluorescence originates from high vibrational levels of theE(0+) state (v′ ≈ 110–205) and terminates in the continuum of the ground electronic state. TheEstate is quite tightly constrained in the region 3.1–4.8 Å by the Rittner potential and known RKR points, but detailed fitting of the interference structure provides additional information about the ground state beyond 2.9 Å. The transition dipole moment appears to pass through a broad maximum in thisRrange.

ISSN:0026-8976    

DOI:10.1080/00268978700102901

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Relative values of the total reaction cross-section for the crossed molecular beam K +RI → KI +R(R= CH3, C2H5, C3H7) reactions have been measured at low collision energies. An estimation of the influence of the radical group upon the reaction cross-section was made. AtET= 0·18 eV of collision energy we found 20A2, 30A2and 39A2for the propyl, ethyl and methyl reactions, respectively. These results reveal a larger steric factor with the size of the alkyl group. This is consistent with the (observed) increase in the backward character of the product (KI) centre of mass angular distributions as the reagents' alkyl group size increases.

ISSN:0026-8976    

DOI:10.1080/00268978700102911

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

We report mean field density functional theory results for Lennard-Jones mixtures in straight cylindrical pores. The interaction parameters were chosen to model argon-krypton. We present density profiles, adsorption isotherms and phase diagrams and discuss the effects of temperature and pore size on capillary condensation.

ISSN:0026-8976    

DOI:10.1080/00268978700102921

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Molecular dynamics simulations and self-consistent mean field (SCMF) calculations have been carried out for a relatively simple model for liquid ammonia. The model consists of Lennard-Jones spheres embedded with the dipole moment, the quadrupole moment and the point polarizability of the ammonia molecule. It is shown that the energy, pressure, dielectric constant and radial distribution function given by this model are in good agreement with experimental results for liquid ammonia. The SCMF theory is found to be much less accurate for this system than for the fluids of water-like particles studied previously. We conclude that many-body interactions which are not easily included in an effective pair potential are important for this model and perhaps for liquid ammonia.

ISSN:0026-8976    

DOI:10.1080/00268978700102931

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A new interpretation of the spherically-symmetric pair potential derived by inversion of the thermophysical properties for non-spherically symmetric molecular systems is presented. The interpretation is based on the original inversion equations cast in a form that makes the connection of the potential from inversion to the full anisotropic potential clearer. Tests on potential models confirm the usefulness of the new formulation because, at least for two simple models, the link between the full potential and the potential from inversion is particularly straightforward.

ISSN:0026-8976    

DOI:10.1080/00268978700102941

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The volume and surface area of a fused hard-sphere molecule can be calculated by the usual formula relating the union of a number of sets to their intersections. In principle, this formula includes intersections of all orders; however, we show that, by making use of the properties of certain types of double, triple, quadruple and quintuple intersection, all terms of the fifth and higher order and some terms of lower order can be eliminated from the expansion, leaving only spheres and intersections of two, three or four spheres. Analytical expressions are derived for the volumes and surface areas of intersections of two, three or four spheres with unequal radii; these expressions allow the exact calculation of the volume and surface area of any fused hard-sphere molecule.

ISSN:0026-8976    

DOI:10.1080/00268978700102951

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor