摘要:

This feature article provides an overview of the additional insights that multiphoton excitation methods are providing to our understanding of the spectroscopy and the photophysics of some of the higher excited electronic states of gas phase molecular species.

ISSN:0026-8976    

DOI:10.1080/00268978600100951

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Computer simulations of liquid equilibrium properties and calculations of the gas second virial coefficient have been made using two of the available representations of the nitrogen intermolecular potential of Berns and van der Avoird. One representation (BV) employs a spherical harmonic expansion and the other (BVAA) employs an atom-atom representation of the same potential energy input data. A variant potential (BV(+)) in which the isotropic dispersion coefficientsC8andC10are increased by 10 per cent and 15 per cent, relative to those in the BV potential, has also been studied. The virial coefficients for BV(+), but not for BV and BVAA, do not differ from experiment by more than the estimated experimental errors and there are significant differences between the BV(+), BV, and BVAA values. The liquid simulation results for the thermodynamic properties and radial distribution functions are compared with each other and with literature values obtained from simulations using effective potentials which employ a two centre Lennard-Jones potential plus quadrupole interaction. At given temperature and density the internal energy and pressure differ significantly for BV and BVAA. Although neither is as successful in comparison with experiment as the best effective potentials, the differences between them are not greater than those encountered between extreme results for the different effective potentials. We emphasize that, in contrast to the effective potentials, the BV and BVAA potentials contain no parameters which have been fitted using bulk properties.

ISSN:0026-8976    

DOI:10.1080/00268978600100961

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The influence of long-range intermolecular forces upon the refractive index and optical rotation of molecular fluids is examined using quantum electrodynamics and many-body theory. An expression for this effect, analogous to the McLachlan formula for the dispersion energy, and involving the molecular polarizability and second hyperpolarizability, is derived in the case of a non-polar fluid.

ISSN:0026-8976    

DOI:10.1080/00268978600100971

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

High resolution electronic spectra of the 1–2 and 0–1 bands of theA2Δ-X2Π system of PH+have been recorded by laser photofragment spectroscopy. Nuclear hyperfine structure due to the31P and1H nuclei is resolved and hyperfine parameters for both nuclei in the ground and excited electronic states are obtained. The parameters are discussed in terms of the electronic structure of the PH+molecule.

ISSN:0026-8976    

DOI:10.1080/00268978600100981

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A Monte Carlo simulation of a dilute solution of N2in H2O was performed under canonical (T, V, N) ensemble conditions at 25°C. Two pairwise analytical potential functions (APF), fitted toab initio4–31 G** and 7/3 basis set SCF calculations, and a simple Lennard-Jones potential, fitted to experimental data, were used in three runs of 8000 K steps each. Analysis of the solution from the microscopic point of view was performed through the calculation of a number of radial and frequency distribution functions, subdividing also the solution in shell and bulk regions. Evidences of water structuring promotion by N2are provided. According to the used potentials, the first hydration shell is predicted to include 17 ∼ 20 water molecules, values very close to that characteristic of the corresponding chlatrate. The partial molar energies calculated by the three APFs show that (7/3) potential gives the value (-21·7 ∓ 14·6 kJ mol-1), close to the experimental solvation enthalpy (-10·4 kJ mol-1). On the other hand the statistical analysis shows that (4–31 G**) potential promotes a structuring of the solvent correctly decreasing in the region far from N2.

ISSN:0026-8976    

DOI:10.1080/00268978600100991

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We report rotationally resolved vibrational spectra of the DCL+molecular ion for ν = 1 ← 0 to ν = 7 ← 6 with a Faraday-L.M.R. spectrometer. The ions were generated in a d.c.-excited discharge of the anomalous type near 2 torr total pressure. A small probe modulation coil allows spatial resolution of the concentration profile along the discharge. Comparisons of such profiles between anomalous and normal discharge conditions are presented. Spectroscopic constants for DCl+X2Π3/2are reported.

ISSN:0026-8976    

DOI:10.1080/00268978600101001

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A theory is developed for the isotropic Raman spectrum of nondegenerate modes in polyatomic binary mixtures. Particular emphasis is attached to isotopic binary mixtures and the problem of dipolar resonant transfer. The thermodynamic state dependences of spectral features are investigated in some detail. Attention is focused on quantities which are experimentally accessible by isotopic dilution experiments, in particular the frequency shift of the spectrum consequent upon isotopic dilution, and also the resultant changes in spectral second moments. The theory is compared with some existing experiments on specific systems, and a number of predictions are made which are capable of being tested experimentally.

ISSN:0026-8976    

DOI:10.1080/00268978600101011

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The use of the angular median and related effective spherical potentials to predict thermodynamic properties of nonpolar homonuclear diatomic liquids has recently been shown to be efficient and accurate. Here we compare the results obtained from median-like methods for some other molecular liquids with simulation data. We find impressive agreement for linear triatomic molecules but results for tetrahedral molecules and for the overlap potential are very poor. The characteristic shape of potential energy frequency distributions at fixed separations is suggested as a criterion for the success or otherwise of the median potential.

ISSN:0026-8976    

DOI:10.1080/00268978600101021

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Moments of the time a diffusion process resides in a particular set of states are calculated and it is shown how these may be used to find the probability distribution function of the occupation time. The local time is defined in terms of the limit where the set of states becomes infinitesimal and its moments are calculated. In the limitt→ ∞ it is shown that if the local time exists it is exponentially distributed. The radiation boundary condition is shown to represent killing in local time. The survival probability for a diffusion with reaction at a boundary is related to the transition density for the diffusion in the absence of reaction.

ISSN:0026-8976    

DOI:10.1080/00268978600101031

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The vapour phase HeI photoelectron spectra of Al2O and Al have been recorded using a new multidetector, high temperature photoelectron spectrometer.Ab initiomolecular orbital calculations which include the effects of electron correlation show that the ground electronic state of Al2O has aD∞hequilibrium geometry and, as a result, the four observed photoelectron bands are assigned to ionization from the outermost 5σu, 6σg, 2πuand 4σumolecular orbitals. For atomic aluminium, three bands have been recorded and measurement of their relative intensities allows the Al 3s: 3pphotoionization cross-section ratio to be measured as (0·36 ± 0·04) : 1 at the HeI photon energy. This result has proved useful in interpreting the relative band intensities in the Al2O spectrum.

ISSN:0026-8976    

DOI:10.1080/00268978600101041

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor