摘要:

We have expressed the angular momentum and the internal kinetic energy of a molecule (a system of point masses) in terms of atom-pair contributions, paralleling the use of pairwise additive potential energy functions. The partitioning of the internal kinetic energy into rotational and vibrational contributions is then made following the analysis of Jellinek, J., and Li, D. H., 1989, 98,Phys. Rev. Lett.,62, 241. The resulting expressions contain pair position and velocity variables whose redundancy may be removed by transformation to Jacobi vector coordinates. These expressions should prove especially useful for describing the internal motions of clusters of like atoms.

ISSN:0026-8976    

DOI:10.1080/00268970009483304

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A comparison is made of the accuracy with which the total electronic energy can be calculated by using either the finite basis set approach (the algebraic approximation) or finite difference methods in calculations employing the restricted Hartree-Fock model for the open-shell ground (X2Σ+) states of the Group Ha fluorides BeF, MgF, CaF and SrF. The convergence of the calculations carried out within the algebraic approximation is monitored by employing systematically constructed basis sets of increasing size. By using two different grids, the accuracy of the finite difference calculations has been estimated to be of the order of 10−2μEh. The average difference between the finite basis set and finite difference total Hartree-Fock energies is 2.75 μEh.Dipole moments determined within the algebraic approximation are also compared with the corresponding finite difference expectation values.

ISSN:0026-8976    

DOI:10.1080/00268970009483305

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Interaction induced Raman light scattering is presented as a unique tool for the understanding of solvation processes from the solute's point of view in weakly interacting solute-solvent systems. A review of pertinent literature shows that this technique should be useful at least in single-phase binary mixtures such as supercritical solutions. Methane is used here as a probe molecule at 10mol% concentration (as the solute) and 90mol% CO and CO2are the solvents. The light scattering results, i.e., the dependence of the anisotropic intensities divided by density(I/d)on the density, are interpreted by use of the Duh-Haymet-Henderson closure (bridge) function of the Ornstein-Zernike integral equation. These data, together, are examined in the context of known supercritical solution thermodynamics and statistical mechanical results. It is shown that the light scatteringI/ddata versus density yield maxima in both attractive and repulsive solute-solvent systems. The local number density maxima were found near these same densities by the integral equation calculations for both methane + carbon monoxide or carbon dioxide using only Lennard-Jones single-centre parameters as input. The methane + carbon monoxide system is identified as weakly attractive (augmenting), whereas the methane + carbon dioxide system is identified as repulsive (avoidance).

ISSN:0026-8976    

DOI:10.1080/00268970009483306

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The potential energy surfaces of the Ca+-H2complex are calculated using the internally contracted multireference CI method (ICMR CI) and complete active space SCF (CAS SCF) reference wave functions. The calculations involve both the ground and the excited states correlating to (3d)2D and (4p)2P Ca+terms and are carried out forC∞vand C2vconfigurations. Anisotropy of the potential surfaces has also been analysed by computing the interaction energy for some representative points as a function of the angle between the H2molecular axis and the Ca+—centre of mass of H2bond axis. The calculations have revealed the existence of a conical intersection of the lowest excited (3d)2B2potential surface with the ground state one. The obtained global energy minimum of the (3d)2B2potential surface lying 0.683 eV below the asymptote indicates a possible stabilization of the Ca+-H2complex towards formation of an exciplex in the (3d)Ca+-H2(v= 0) collision process. The dependence of the vibrational energy levels of H2on the distance from Ca+in the C2vconfiguration has also been studied.

ISSN:0026-8976    

DOI:10.1080/00268970009483307

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Statistical geometry provides exact relations between the thermophysical properties of hard sphere systems and various geometric quantities. Utilizing recently derived relations that describe multicomponent hard sphere systems, we derive two new expressions which place rigorous constraints on the behaviour of geometric quantities across a first-order phase transition. Some implications of these constraints for a binary mixture of additive hard spheres are discussed.

ISSN:0026-8976    

DOI:10.1080/00268970009483308

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A method to obtain (approximate) analytical expressions for the radial distribution functions in a multicomponent mixture of additive hard spheres that was recently introduced is used to obtain the direct correlation functions and bridge functions in these systems. This method, which yields results practically equivalent to the generalized mean spherical approximation and includes thermodynamic consistency, is an alternative to the usual integral equation approaches and requires as input only the contact values of the radial distribution functions and the isothermal compressibility. Calculations of the bridge functions for a binary mixture using the Boublik-Mansoori-Carnahan-Starling-Leland equation of state are compared to parallel results obtained from the solution of the Percus-Yevick equation. We find that the conjecture recently proposed by Guzman and del Rio (1998, 98,Molec. Phys.,95, 645), stating that the zeros of the bridge functions occur approximately at the same value of the shifted distance for all pairs of interactions, is at odds with our results. Moreover, in the case of disparate sizes, even the Percus-Yevick bridge functions do not have this property. It is also found that the bridge functions are not necessarily non-positive.

ISSN:0026-8976    

DOI:10.1080/00268970009483309

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A study was conducted on the optical absorption spectra ranging from 233 to 285 nm, which were taken in a region close to the source of evaporation of Cu, in low-pressure helium gas of 100 Torr. Eight band systems for Cu2dimers designated as system 1 through 8 were identified. The spectroscopic constants for the band origins were derived as follows: ṽ ≈ 42 200 cm−1for system 1, ṽ00= 41 604.74cm−1for system ṽ00= 39 606.70cm−1for system ṽ00= 38 124.32cm−1for system4, ṽ00= 38 048.65 cm−1for system 5, 98, ṽ00= 36 834.22cm−1for system 6, ṽ00= 36 341.55 cm−1for system 7 and ṽ00= 36 174.99cm−1for system 8. For all cases in which vibrational constants of the lower state could be determined, it was found that the transition originated from the ground state of Cu2.

ISSN:0026-8976    

DOI:10.1080/00268970009483310

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Quadrupole moment and dipole polarizability tensor components are calculated at the correlated complete-active-space self-consistent-field (CASSCF) and complete-active-space perturbation-theory (CASPT) levels for2P states of O−, F, Ne+, Na2+, S−, Cl, Ar+, 98,K2+, Se−, Br, Kr+, Rb2+and3P,1D,1S states of O−, F+, Ne2+, Na3+, S, Cl+, Ar2+, K3+, Se, Br+, Kr2+, Rb3+. Relativistic corrections are included perturbatively for the 34- and 35-electron systems.

ISSN:0026-8976    

DOI:10.1080/00268970009483311

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The interaction of small Pt-Re clusters with H2is reported here throughab initiomulticon-figuration self-consistent field (MC-SCF) calculations, plus extensive multireference configuration interaction (MR-CI), variational and perturbative calculations. These calculations provide a cluster model for the activation of hydrogen by Pt-Re bimetallic catalysts. It was found that the6S(5d56s2) Re atom ground state needs an important activation to induce very weak capture of separated hydrogen atoms, whereas in the lowest excited states the activation energies are small or zero, with a very reasonable depth of well. The four lowest states of Pt-Re were found to be4Σ+,6Πyz,Σ+and6Πxz. Pt-Re interaction with H2has been studied from both metal ‘sides’. It was established that Pt-Re with the platinum side in the ground electronic4Σ+state and in the lowest6Π+excited states is able to capture H2molecules without activation, whereas in the6Πyzand6Πxzexcited states there is no capture. The rhenium side of Pt-Re in its four lowest states considered cannot capture the H2molecule. The interaction of Pt2-Re with H2was studied also. For the ground2B2electronic state and the low lying2A1electronic state the platinum moiety can spontaneously capture and break H2. The rhenium side of Pt2-Re(B2), however, can capture H2only after surmounting a small barrier, and the excited Pt2-Re(2A1) can spontaneously capture H2. For Pt2-Re in its low lying4A1electronic state both metal sides capture and break H2after surmounting a small barrier.

ISSN:0026-8976    

DOI:10.1080/00268970009483312

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor