摘要:

The temperature dependences of the proton nuclear magnetic resonance (NMR) spectra of the solutes 1,3,5-trichlorobenzene, metadichlorobenzene, orthodichlorobenzene, 1,3-bromochlorobenzene, benzene and 2-butyne have been studied in the special ‘zero electric field gradient’ mixtures 55 wt% 1132-N-(4-ethoxybenzylidene)-4'-n-butylaniline (EBBA) and 70 wt% (4-n-pentyl)-4'-cyanobiphenyl-EBBA. The order parameter matrices obtained for each solute from an analysis of the NMR spectra indicate that the solutes experience a similar anisotropic potential in both mixtures.

ISSN:0026-8976    

DOI:10.1080/002689797172435

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A gas-phase resonance Raman spectrum of chloroiodomethane has been obtained with excitation in the A-band absorption with similar resolution and the same experimental apparatus used to obtain solution-phase A-band resonance Raman spectra of chloroiodomethane reported previously. This allows a careful and detailed comparison of the gasand solution-phase chloroiodomethane A-band resonance Raman spectra and their associated short-time photodissociation dynamics. The gas-phase A-band resonance Raman spectrum has four Franck-Condon active vibrational modes and a noticeable degree of multidimensionality in its photodissociation reaction. The A-band gas-phase resonance Raman intensities and absorption spectrum were simulated using a simple model and time-dependent wave-packet calculations. The motion of the wave packet on the excited state gas-phase potential surface was converted from dimensionless normal coordinates into easy-to-visualize internal coordinates using the results of normal coordinate calculations. The A-band early-time photodissociation dynamics are very similar to those of the solution phase in that the C–I bond lengthens, the I–C–Cl and H–C–I angles become smaller, and the H–C–Cl angles become larger. These short-time photodissociation dynamics are consistent with a simple impulsive ‘semirigid’ radical model description of the photodissociation.

ISSN:0026-8976    

DOI:10.1080/002689797172444

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The free surfaces of two binary liquid mixture systems over the whole range of bulk molar composition have been studied using HeI photoelectron spectroscopy in a thin, fast flowing jet arrangement. The spectra of the first group of mixtures, benzyl alcohol and formamide, are found to be deconvolutable by a weighted sum of the pure component spectra. Slight deviations in the procedure allow an estimate to be made of the surface orientation of single benzyl alcohol molecules on top of the formamide solvent. The relative surface composition in the top layer is extracted by the deconvolution procedure. Time relaxation of the surface composition is observed with time constants of the order of several tens of mus. The results of the second group of mixtures, water and formamide, show more complicated features, with one component rapidly evaporating on the time scale of the experiment. The relative surface composition is estimated by a constrained deconvolution involving mainly the first two ionization bands of the components. The location of individual peak structures changes markedly with the mixture composition ratio. The energy values of the first ionization bands indicate a solvent-solvate transition near a 2:1 to 3:1 bulk molar fraction of water. Time relaxation of the surface composition is observed also in these mixtures.

ISSN:0026-8976    

DOI:10.1080/002689797172453

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The hot infrared transitions of C2D6from the υ4(A1u) to the υ4+ υ6(A2g) and υ4+ υ8(Eg) vibrational states, observed from 960 to 1180 cm−1, have been rotationally analysed on a high-resolution Fourier transform spectrum (full width at half-maximum about 0·0030 cm−1). The vibration-rotation interactions affecting the upper vibrational states are very similar to those of the corresponding cold system. A strongx,yCoriolis interaction between υ4+ υ6and υ4+ υ8, withK-level crossing, generates large displacements of the rotational components of both vibrational states, tuning them to additional local resonances in several spectral regions. Thuslresonances with Δl= ±2, Δk= ±1 occur within υ4+ υ8. Ax,yCoriolis-type resonance between υ4+ υ8(−l,K− 1) and υ3+ 2υ4(K) occurs atK= 11,12,13, and a further coupling of υ4+ υ8(+l,K+ 1) and υ3+ 2υ4(K+ 3) is most effective atK= 11 and 12. These resonances induce torsional splittings on the perturbed levels of υ4+ υ8and allow us to determine the torsional splittings in the υ3+ 2υ4state. The vibration-rotation constants of υ4+ υ6, υ4+ υ8and υ3+ 2υ4, several interaction parameters and the torsional splitting of υ3+ 2υ4have been determined by least-squares fit of 1391 observed transition wavenumbers, with an overall standard deviation σ = 0·75 × 10−3cm−1. The vibrational wavenumbers found for the four torsional components of (υ3+ 2υ4)− υ4are υ(E3d) = 1040·961 82(809)cm−1, υ(A3d) = 1041·218 27(865)cm−1, υ(E3s) = 1041·225 23(662)cm−1and υ(A1s) = 1041·407 77(633)cm−1. These are anomalous for both the order of the torsional components and the magnitudes of their separations. We believe that this is mainly due to the interactions of υ3+ 2υ4with the torsional manifolds with υ3= 0 and υ3= 2, through the vibration-torsion Hamiltonian term (∂V6/∂q3)q3cos (6γ)]/2. The further observation of a few doublets of υ8and υ3+ υ4at resonance provides information on the torsional splitting of the latter state.

ISSN:0026-8976    

DOI:10.1080/002689797172462

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A family of primitive models of water, which differ from one another in the number and location of interaction sites, is introduced and their properties examined by Monte Carlo simulations. In addition to the existing symmetric 5-site model, which has its origin in the ST2 potential, asymmetric 3- and 4-site descendants of TIPS potentials are introduced along with an extended 5-site model which incorporates a short-range repulsion between the like sites. The structure of the fluids defined by the primitive models has been investigated in detail by computing site-site correlation functions, both at high and low densities, and the angular distribution of particles engaged in hydrogen bonding. For completeness, the thermodynamic properties have also been computed. It transpires that the extended 5-site model, due to its enlarged range of the hydrogen bond interaction, clearly is much better than all the other models. It is able to reproduce evensemi-quantitativelythe structure of real water, and thus seems well suited to all potential applications involving water, including perturbation theories using the extended model as a reference fluid.

ISSN:0026-8976    

DOI:10.1080/002689797172471

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

An analytic equation of state for the hard core Yukawa fluid is presented. This explicit, nonempirical equation of state is based on the inverse temperature expansion of the free energy from the mean-spherical approximation (MSA). This equation of state yields an excellent description of the pressure when compared with simulation results. The critical point properties obtained using this equation of state are almost identical to those obtained from the exact MSA. The vapour-liquid coexistence is also studied; the resulting phase diagram agrees very well with the result from the Gibbs ensemble simulation, except in the vicinity of the critical point.

ISSN:0026-8976    

DOI:10.1080/002689797172480

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A Fourier transform interferometer was used to record the slit-jet cooled overtone absorption spectrum of12C2H4between 3800 cm−1and 7900 cm−1, at a spectral resolution of 0·02 cm−1. The experimental set-up and its technical performance are described. The spectral data are exemplified with the help of six selected bands, at 4288·40, 4312·63, 4321·77, 4328·65, 4514·657 and 6150·978 cm−1, whose rotational analysis is performed for the first time. The two lower energy bands, bothbtype, were not previously reported at all. They are tentatively assigned to the anharmonically resonant pair υ2+ υ6+ υ12and υ6+ 2υ10+ υ12.

ISSN:0026-8976    

DOI:10.1080/002689797172499

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Dipole oscillator strength distributions have been constructed for acetone, acetaldehyde and formaldehyde, by using constrained least-squares methods, experimental and mixture rule dipole oscillator strength data, and molar refractivity data. The distributions have been used to evaluate recommended values for a wide variety of isotropic dipole oscillator strength sums, logarithmic dipole sums, and mean excitation energies for each molecule. Often these results are the only (reliable) values available for many of these properties which are of importance in a variety of research areas.

ISSN:0026-8976    

DOI:10.1080/002689797172507

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

13C NMR spin-lattice relaxation timesT1of quinoline (1) of some of its methyl derivatives (quinaldine (3), lepidine (4), 6-methylquinoline (5), 7-methylquinoline (6)) of isoquinoline (2), and of two quinoline related compounds having two nitrogen atoms in one fused sixmembered ring skeleton (quinazoline (7), quinoxaline (8)) have been measured in pure liquid form as a function of temperature. The temperature range is not the same for all the compounds. It is at least 46 K for (7) and it reaches 93 K for (4). lnT1is plotted as a function of the inverse of the absolute temperatureT−1. For (2), (6), (7) and (8) the data can be accounted for by only one activation energy, for (1), (3), (4) and (5) by two activation energies one above temperatureTt, one below. For all these compounds the high temperature relaxation corresponds to an energy barrier which is less than 20·5 kJ mol−1, and the low temperature process (when a two energy barrier regime exists) corresponds to an energy barrier close to 30 kJ mol−1. For quinoline and isoquinoline, the saturated specific heatCsplotted as a function ofTexhibits behaviour similar to that of lnT1studied as a function ofT−1. The results reported here suggest the existence of a dynamical transition in the liquid state at a given temperature, a process somewhat similar to that proposed for some super-cooled liquids.

ISSN:0026-8976    

DOI:10.1080/002689797172516

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Tetra-p-tolyl and tetrathienyl substitution of manganese(III) porphyrins in charge-transfer compounds with organic acceptors like tetracyanoethylene is used to modify molecular packing of ferrimagnetically correlated chains in the solid. Ferri- and antiferromagnetically ordered compounds and also borderline situations are realized. The strong influence of the solvent used for crystal growth is exemplified.

ISSN:0026-8976    

DOI:10.1080/002689797172525

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor