摘要:

The parity non-conservation (PNC) terms of the molecular Hamiltonian are presented, including the nuclear anapole term. The formulae giving the PNC contribution to the nuclear magnetic shielding tensor σ, to the indirect spin—spin coupling tensorJand to the spin—rotation tensorCare derived from a perturbation calculation. Some remarks concerning the tensor symmetry are given.

ISSN:0026-8976    

DOI:10.1080/00268979609484479

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Calculations are reported of the mean polarizabilityand the mean second hyperpolarizabilitywhich emanate from the interaction between two helium atoms. The results are based on three levels of calculation (SCF, MP2 and MP4) and for a wide range of interparticle separations. The values ofand, after correction for basis set superposition error, are used (a) to discuss long-range dispersion and dipole—induced-dipole effects, and (b) to assess the approximate formulas for these effects which have been obtained from perturbation theory as opposed to the present ‘supermolecular’ calculations. The results are used also to determine the second dielectric virial coefficient and the second virial coefficient of the second hyperpolarizability; these are found to be −0·0614 cm6mol−2and −1·41 cm3mol−1, respectively.

ISSN:0026-8976    

DOI:10.1080/00268979609484480

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The spectrum of the weakly bound complex CO-OCS has been measured in the infrared using direct absorption diode laser spectroscopy in a supersonic jet, and in the microwave region using a pulsed nozzle Fourier-transform instrument. In addition, microwave spectra of the two isotopomers13CO-OCS and CO-OC34S were recorded. A T shaped structure has been determined with the carbon atom in CO closest to the OCS (RMS angle ±20·5° with respect to the intermolecular axis) and the sulphur end of OCS pointing away from CO (vibrationally averaged angle 105·7°). The ground state centre of mass separation is 4·17 Å. The effective structure is rationalized by a simple potential incorporating a distributed multipole analysis of the electrostatic charge distribution, distributed dispersion contribution and a cylindrical hard core repulsion, with discussion of the implications for the potential of including correlation effects in the CO multipole.

ISSN:0026-8976    

DOI:10.1080/00268979609484481

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The microwave spectrum of OCS trimer, measured between 6 GHz and 18 GHz using Fourier-transform microwave spectroscopy, is consistent with a very asymmetric rotor,k= 0·18.A- andc-type transitions are observed with many lines showing a fine doubling of less than 20 kHz. A fit of average line positions to Watson A reduction (IR) rotational parameters gives;A= 847·97958(2),B= 736·17579(2),C= 574·32591(1) MHz, ΔJ= 0·45440(9), ΔJK= 0·1572(5), ΔK= 0·3010(5), δJ= 0·06797(4), δK= 0·0339(3)kHz. From a sum of electrostatic and Lennard-Jones pair interaction potentials, the model trimer equilibrium structures are chiral, suggesting the observed splitting is the result of tunnelling interconversion between enantiomers. A scheme employing the recursion relation for associated Legendre polynomials is used to extend the distributed multipole method for the electrostatic interaction between linear molecules to include multipole moments up to the highest order available fromab initiocalculations.

ISSN:0026-8976    

DOI:10.1080/00268979609484482

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The electric hypermagnetizabilities and nuclear shielding polarizabilities of the CO and CH4molecules are computed using multiconfigurational linear response theory and a finite field method, in a mixed analytical-numerical approach. Extended sets of magnetic field dependent basis functions are employed. The use of the natural connection ensures good accuracy of the magnetic properties after numerical differentiation. The CO data are compared with other correlated literature results, and for CH4the first correlatedab initioestimates of both properties are presented.

ISSN:0026-8976    

DOI:10.1080/00268979609484483

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The dissociation dynamics for NH3(Ã) → H + NH2([Xtilde]) have been calculated using time-dependent quantum theory and anab initiopotential in the three dimensions of NH stretching, the out-of-plane motion and HNH bending. These calculations use a Hamiltonian for a combination of internal coordinates for NH2and Jacobi coordinates for the relative motion of the H atom. Inclusion of HNH bending removes most of the gross inaccuracies present in earlier two-dimensional calculations. The calculated dissociation rates are, in general, lower than observed experimentally, indicating that the effective potential barrier to dissociation is too high. This is attributed to the influence of neglected vibrations. Excited state vibronic resonance energies, resulting product-state population distributions and state-dependent product recoil anisotropy factors compare favourably with experiment, permitting a detailed interpretation of the dissociation dynamics. Dissociation through the 00and 21levels of the à state proceeds by quantum tunnelling through the barrier. Scattering of the outgoing waves at a conical intersection of the à and [Xtilde] adiabatic surfaces then accelerates the out-of-plane motion to generate high rotation of NH2about itsainertial axis. Forces at this intersection also generate modest excitation of NH2bending. For all higher levels, dissociation is mediated by intramolecular vibrational energy redistribution, two quanta ofv'2being converted to NH stretching. A local mode calculation of the NH stretching resonance confirms a proposed assignment of broad bands in [Ctilde]′ → à emission spectra to thev'1modes of à state NH3and ND3. The recoil anisotropy calculated for each product state gives a satisfactory account of the extreme range of values observed experimentally. Comparison of the calculations with a semi-classical model supports an earlier assumption that the conical intersection of adiabatic surfaces acts as a defining point for most trajectories leading to dissociation.

ISSN:0026-8976    

DOI:10.1080/00268979609484484

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

New data analysis by ourselves for the liquid crystalp-methoxybenzylidine-p-n-butylaniline (1994,Molecular Physics,81, 1017) points out a regrettable error in our previous analysis using the Nordio model. The usefulness of analysing globally deuteron relaxation data is examined here. We believe that both the Nordio model and the third rate model are good in describing rotational diffusion motion in liquid crystals.

ISSN:0026-8976    

DOI:10.1080/00268979609484485

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In complexes belonging to the series B ··· X2(X = halogen), the measured nuclear quadrupole coupling constants show a consistent trend: after allowing for zero-point angular oscillation of X2, χ(X) for the inner nucleus is larger in magnitude than in free X2while for the outer nucleus it is smaller by approximately the same amount. These observations are consistent with supermolecule calculations reported here and with two simple models. The Townes-Dailey model gives the (small) fraction δ of an electron shifted from the inner to the outer atom on formation B ··· X2. The long-range model of intermolecular forces allows deduction of a Sternheimer-like response propertygzz,zof free X2from the observed variation of δ with B. For Cl2, the value deduced forgzz,zis 65 au, in reasonable agreement with a previousab initioresult of 45·3 au.

ISSN:0026-8976    

DOI:10.1080/00268979609484486

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Doppler-free Stark Spectra of the 401band of the Ã1A2—[Xtilde]1A1system of thioformaldehyde have been obtained using the technique of intermodulated fluorescence. Fully resolvedmstructures have been obtained for ten lines with linewidths of about 5 MHz. Theacomponent of the dipole moment of the molecule in the excited state is 0·815 ± 0·020 Debye, but values from 0·77 D to 0·93 D have been derived from some of the Stark patterns depending on the degree of mixing of the excited-state levels with high rovibronic levels of the ground state.

ISSN:0026-8976    

DOI:10.1080/00268979609484487

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Exact and local spin density approximation (LSDA) exchange energy density functionals in the Coulomb-attenuated Schrödinger equation (CASE) approximation are constructed. When expressed as asymptotic series in the attenuation parameter ω, their leading terms are identical. If a Gaussian basis set is used, the terms in the exact series (but not the LSDA series) can be evaluated analytically, i.e. without resorting to quadrature on a grid.

ISSN:0026-8976    

DOI:10.1080/00268979609484488

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor