摘要:

An experimental and theoretical study has been performed on dissociation pathways of the FBrCO molecule. Experimentally, the infrared multiphoton dissociation technique has been used to dissociate FBrCO molecules and the products analysed using Fourier transform infrared spectroscopy. The threshold intensity for the multiphoton dissociation of FBrCO has been determined to be 143·4 ± 15 MW cm-2. Theoretically,ab initiomolecular orbital theory calculations at the second order Møller-Plesset level of theory have been performed to estimate the energetics of the dissociation pathways of FBrCO. Both experimental and theoretical results suggest that the most favourable dissociation pathway on the ground state potential energy surface is the Br-C bond fission process to yield Br + FCO.

ISSN:0026-8976    

DOI:10.1080/00268979300101031

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A variational method for calculating vibrational energy levels of polyatomic molecules is developed and applied. Using this new approach energy levels (and wavefunctions) may be determined without storing Hamiltonian matrix elements. An explicit finite representation of the Hamiltonian is circumvented by representing basis functions on an evenly spaced grid, employing Fourier transforms to evaluate the action of the Hamiltonian operator on the basis functions, and using the Lanczos algorithm to calculate eigenvalues. Unhampered by the need to store a finite representation of the Hamiltonian, the method should make it possible to calculate many energy levels of molecules with many vibrational degrees of freedom.

ISSN:0026-8976    

DOI:10.1080/00268979300101041

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The conformations of fully protonated (H2SA), fully deprotonated (SA=) and monoprotonated (HSA-) succinic acid have been investigated by means of nuclear magnetic resonance spectroscopy in liquid crystal mesophases (Licry-NMR). H-H and13C-H direct dipolar couplings have been determined by measuring1H-NMR and13C-NMR spectra from quaternary nematic-lyotropic solutions of myristyltrimethylammonium bromide (MTAB), decanol, deuterated water and succinic acid (in each of its three different protonated forms). Direct dipolar couplings have been used to investigate the conformational equilibrium of the molecule in its three different protonation forms. Data could be interpreted in terms of a single conformation for each of the investigated forms. The dihedral angle between the H3-C5′-C5and the C5′-C5-H1planes gradually increases when going from the fully protonated H2SA species to the SA=ions. Our findings are different from those obtained by other authors by analysis ofJijcouplings. In that case an equilibrium conformation between the gauche and trans conformers had been obtained.

ISSN:0026-8976    

DOI:10.1080/00268979300101051

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A Gibbs ensemble (GE) Monte Carlo technique to evaluate phase equilibria for systems in which a thermodynamic model describes accurately one of the coexisting phases is detailed. Such a simulation is conducted in much the same manner as a standard GE simulation: particles are moved about within one phase, and volume and particles are exchanged between the phases. However, with the proposed modification, one of the phases becomes a ‘virtual’ phase, and no account is made of particle positions within it. When formulating the acceptance criteria for particle and volume exchange, the residual free energy change of the virtual phase plays the role of the intermolecular potential energy change normally used in a GE simulation. We demonstrate the technique by computing the coexistence envelope of a van der Waals fluid. In the more interesting case of the Lennard-Jones fluid we show that when using a fifth-order virial model for the vapour, the technique accurately reproduces the phase envelope for temperatures to within 5% of the critical, while requiring substantially less computation than the standard GE simulation. Other potential benefits of the technique are discussed.

ISSN:0026-8976    

DOI:10.1080/00268979300101061

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Potential-distribution theory and a cumulant analysis are used to derive a simple relation for the temperature dependence of the solubility of a solute in a liquid solvent. It is shown that infinite dilution thermodynamic properties at constant volume and at constant pressure can be deduced with accuracy over a broad range of temperature by just initiating two simultaneous cumulant expansions from a single state point conveniently chosen. The method is applied to the case of nitrogen in water and very good agreement is obtained with recent Henry's constant data extending from the triple point (273 K) to 10 degrees below the critical point of water (Tc⋍ 647 K). Uses and misuses of the method are presented, while the relationships with empirical correlations proposed in the literature are emphasized and discussed.

ISSN:0026-8976    

DOI:10.1080/00268979300101071

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

NMR water proton transverse and longitudinal relaxation time measurements are reported for aqueous suspensions of silica powder of varying silica/water ratios. For compositions ranging from the dilute suspension to the saturated randomly packed powder the relaxation is sensitive to the particle distribution function. A simple cluster model is developed to interpret the results in this regime. For compositions ranging from the saturated randomly packed suspension to the almost dry powder the relaxation is sensitive to the distribution of water throughout the packed solid matrix. A simple capillary model is developed for this regime. The models are tested on two sizes of silica particle, and the potential of NMR for studying other types of solid suspension is discussed.

ISSN:0026-8976    

DOI:10.1080/00268979300101081

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The thermal emission spectrum of TiS has been recorded with Fourier transform spectroscopy in two different regions, 10 000–12 600 cm-1and 6 000–8 600 cm-1, with a resolution of 0·05 cm-1. The first region covers the C3Δ-X3Δ system while the second region covers the previously unobserved A3Φ-X3Δ and E3Π-X3Δ systems. Lines from 18 different vibrational bands were included in the analysis. Of these, 9 belong to the C3Δ-X3Δ system, 8 to the A3Φ-X3Δ system, while only the (0, 0) band was observed in the E3Π-X3Δ system. No satellite transitions were observed. Molecular constants have been determined for the four states. A perturbing state causing the observed local perturbations in the C3Δ1substate is suggested. The electron configurations of the four states have been discussed in terms of observed bond lengths.

ISSN:0026-8976    

DOI:10.1080/00268979300101091

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A numerical study of the stability of theAB13crystal structure in a mixture of dissimilar hard spheres is reported. This crystal structure has recently been observed by Bartlett and coworkers in experiments on suspensions of colloidal hard-sphere mixtures. We find that, over a range of densities and diameter ratios, theAB13phase is thermodynamically stable both with respect to the fluid mixture and the crystal structures of pureAand pureB. A tentative phase diagram is presented.

ISSN:0026-8976    

DOI:10.1080/00268979300101101

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A model is worked out for the interpretation of the magnetic properties of polyoxovanadium clusters, containing both localized and delocalized vanadium(IV). The role of exchange and delocalization is worked out parametrically for two model systems containing four localized and two and four delocalized vanadium(IV) over eight sites respectively. The effect of vibronic coupling is also taken into account.

ISSN:0026-8976    

DOI:10.1080/00268979300101111

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An efficient algorithm, a hybrid of the Picard-type and Newton-Raphson (NR) methods, is developed for solving the reference hypernetted-chain (RHNC) theory for non-spherical particles near a uniform planar wall. The basic idea of the algorithm is also applicable to non-spherical particles near a large macroparticle at infinite dilution. The problem of dipolar hard spheres near a hard wall is chosen here as an example system. A feature of the algorithm is that the Jacobian matrix is determined in the bulk calculation and serves as part of the input data for the wall calculation. Hence, the convergence is achieved in only a single iteration in the inner NR loop regardless of the initial values of the iteration variables. It is shown that the great advantage of the constant Jacobian matrix can be preserved even for general cases of other particle-particle and wall-particle interactions. In the course of the study, we encounter a singular behaviour of the RHNC theory for bulk dipolar hard spheres. Keeping the reduced density, we continue to increase the reduced dipole moment. Then, at a certain point the projections of the rotational invariant expansion of the total correlation functionhmm0(r) (m≠ 0;m= 1,2,3, …) become infinitely long ranged, which causes divergence of their Fourier transforms at zero wave-number,ħmm0(0). The static dielectric constant and the heat capacity also diverge at that point. The singular behaviour implies the growth of the strong, long-ranged orientational order favouring parallel configuration, and represents a stability limit of the isotropic phase.

ISSN:0026-8976    

DOI:10.1080/00268979300101121

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor