摘要:

In previous work we have established that the electronic wavefunction for HD+becomes extremely asymmetric as the lowest dissociation limit, H++ D(1s), is approached, with the electron tending to become localised at the deuteron. Recent improvements in our experimental techniques have resulted in a 104increase in sensitivity, and we have now located the 22-17 band in HD+, and remeasured the 21-17 band with greatly improved resolution. The increase in sensitivity has also enabled us to make radiofrequency/infrared double resonance measurements in the 21-17 band. We now present a detailed analysis of the hyperfine structure in these bands, and compare the hyperfine constants derived with the results of new ‘full two state’ calculations.

ISSN:0026-8976    

DOI:10.1080/00268979100100531

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Reactive scattering of F atoms with C3H5I molecules has been studied at an initial translational energyE∼ 38 kJ mol-1using a supersonic beam of F atoms seeded in He buffer gas and atE∼ 12 kJ mol-1with Ne buffer gas. The centre-of-mass angular distribution of IF scattering atE∼ 38 kJ mol-1shows peaking in the forward and backward directions which is consistent with reaction via a short-lived F-I-C3H5complex with a lifetime less than one rotational period. The angular distribution atE∼ 12 kJ mol-1has a broad peak in the forward direction. The extended microcanonical theory shows that only a minor fraction of scattering at high initial translational energy may be identified with the precessional motion of the F-I-C3H5product transition state formed in large impact parameter collisions. However, a major fraction of scattering atE∼ 38 kJ mol-1and all the scattering atE∼ 12 kJ mol-1may be described by phase space theory. The product translational energy distributions indicate that energy is not randomized over internal modes of the intermediate complex in accord with previous laser-induced fluorescence measurements of the IF product vibrational state distribution. However, the overall distribution of internal energy which determines the product angular and translational energy distributions is compatible with the microcanonical distribution for an effective number of internal degrees of freedom.

ISSN:0026-8976    

DOI:10.1080/00268979100100541

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

An analytic equation of state of an arbitrary primitive model of associated liquids, based on Wertheim's thermodynamic perturbation theory, is given. The equations for the models of ammonia (spherical core) and methanol (non-spherical core) are then examined in detail, and it is shown that they give only one fluid phase. An attempt is made to link this result to the H-bond network: using the Cayley tree approximation no percolation threshold has been found for these two models, i.e. their molecules may form clusters of finite size only. This finding contrasts with the result for the model of water which may form infinite clusters and exhibits the liquid-gas phase transition.

ISSN:0026-8976    

DOI:10.1080/00268979100100551

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A framework is presented to calculate rotational line intensities in doubly-enhanced four-wave mixing (DEFMI)-spectroscopy for diatomic molecules following Hund's case a. The results are extended to include cases where one of the two intermediate states is slightly displaced from exact resonance. The model is shown to describe correctly the intensity patterns observed in DEFMI-spectra of CO. It is also successfully applied to evaluate the two-photon resonance-enhanced third harmonic generation (THG) line intensities in a case where a molecular transition is accidentally near-resonance at the three-photon level. Finally, it is shown that saturation greatly reduces the expected intensities if high laser powers are used.

ISSN:0026-8976    

DOI:10.1080/00268979100100561

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A perturber that lies on a reflection plane of a chromophore gives no net helical character to transitions of that chromophore, and hence no circular dichroism spectrum. If, however, a molecule has two such substituents then it may in fact be chiral, with its circular dichroism resulting from the concerted coupling of both substituents to the transition of interest. In this paper the circular dichroism spectra of olefin and carbonyl molecules of this kind are analysed and related to the molecular geometry using an extended independent systems perturbation approach.

ISSN:0026-8976    

DOI:10.1080/00268979100100571

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

This paper reports the predictions of a non-local free energy density functional theory of the ion density and the mean electrostatic potential profiles of the restricted primitive model of the electrical double layer. Results for unsymmetrical 2:1 electrolytes predicted by three different non-local free energy density functional approximations are compared with those of Monte Carlo simulations and of the modified Gouy-Chapman theory. The diffuse layer potentials are also compared with those of some recent theories of the electrical double layer. In the free energy density functional theory the hard sphere repulsive contribution to the Helmholtz free energy is represented by non-local density functional models that have appeared in previous work. The mean spherical approximation for the bulk electrolyte is used to model the electrostatic part of the non-uniform ion-ion correlations present in the interface. In the case of singly charged counterions the agreement between the free energy density functional theory and the Monte Carlo simulations is within a few per cent at the densities and surface charges studied. In the case of doubly charged counterions, however, the agreement is poor at low electrolyte concentrations, although good at high concentrations. The density functional theory correctly predicts the existence of an extremum in the diffuse layer potential as a function of the surface charge density.

ISSN:0026-8976    

DOI:10.1080/00268979100100581

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Corresponding-states theories fail to predict the large difference observed between n-butane and isobutane viscosities at similar reduced conditions. To investigate the molecular cause of these structural effects upon viscosity, nonequilibrium molecular dynamics simulations of Lennard-Jones site-site models representing n-butane and isobutane are performed over much of the density range for which experimental data are available. Simulated viscosities at zero shear agree very well with experimental data over the entire density range. Site size, non-equilibrium molecular alignment and molecular geometry are the primary factors causing both the similarities and differences between the isomers' viscosity and rheology.

ISSN:0026-8976    

DOI:10.1080/00268979100100591

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Procedures allowing for great simplification of the cross-peak multiplet structure in COSY-type two-dimensional NMR spectra are described on the basis of symmetry considerations. Bilinear mixing is discussed in detail and its features are elucidated experimentally. Maximum simplicity is obtained with planar mixing—a new method that is compared with isotropic mixing in total correlation spectroscopy.

ISSN:0026-8976    

DOI:10.1080/00268979100100601

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A brief summary is given of our theoretical approach to the statistical description of interacting Brownian particles. For the discussion of particle transport processes on the Smoluchowski level a hierarchy of coupled diffusion-like equations in configuration space for the reduced particle density functions and the corresponding particle flows is derived. Non-equilibrium processes are taken into account by means of linear perturbation theory. Applying the direct correlation force formalism, the hierarchy is cut off by replacing the three-particle density functionnabc(r1,r2,r3,t). Here closure relations between the direct correlation force andnab(r1,r2,t) have to be added. Specializing the brownons to hard spheres and neglecting the hydrodynamic interaction, the two-particle density function is evaluated from the well-known equilibrium PY approximation and (as a first step) from the low-density limit of the non-equilibrium closure. Using a linear response theory of particle transport, the self-diffusion coefficient in a one-component hard sphere system of Brownian particles is calculated through a formal non-equilibrium picture based on tracer diffusion.

ISSN:0026-8976    

DOI:10.1080/00268979100100611

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We describe a non-equilibrium molecular dynamics algorithm for thermal conductivity/diffusion in binary simple fluid mixtures. The external field drives both a heat current and a diffusive current permitting calculation of the linear response coefficientsLQQandL1Qwhich are required for the calculation of the thermal conductivity and the thermal diffusion (Soret effect). The algorithm is momentum-preserving and has the interesting property it does not satisfy the adiabatic incompressibility of phase space. However, it does generate the correct response.

ISSN:0026-8976    

DOI:10.1080/00268979100100621

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor