摘要:

A general expression is developed for the time development of the alignment of an ensemble of isolated molecules having two random internal spins when the ensemble is optically pumped by absorption of a linearly polarized light pulse. This derivation assumes that the internal spin structure (fine structure/hyperfine structure) is coherently excited and is not resolved. As an example the pulsed infrared excitation of hydrogen fluoride is considered, in particular the vibration-rotation transition HF(ν″ = 0,N″) → HF(ν = 1,N). The presence of the nuclear spinsIH= 1/2 andIF= 1/2 is found to cause a significant reduction in the degree of alignment of the low rotational levels but the extent of depolarization diminishes rapidly with increasingN.

ISSN:0026-8976    

DOI:10.1080/00268978500101121

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

All bound states of the (N2)2dimer are calculated by solving the rovibrational problem for the rigid monomer hamiltonian, using anab initiopotential and a symmetrized product basis of angular momentum and associated Laguerre functions. Next we have evaluated the infrared line strengths for all the symmetry allowed bound-bound transitions, employing the empirical dipole function deduced from the collision induced far infrared spectrum and the N2multipole moment and polarizability derivatives fromab initiocalculations. Thus we have generated the (N2)2dimer far-infrared spectrum, corresponding to pure van der Waals vibrations and rotations, and the mid-infrared spectrum in the region of the monomer fundamental stretch (2330 cm-1). Due to the strong anisotropy of the potential, on the one hand, but the lack of rigidness of the (N2)2dimer, on the other, the spacing between vibrational levels and the shape of the rotational bands and, therefore, the appearance of the infrared spectra is very irregular.

ISSN:0026-8976    

DOI:10.1080/00268978500101131

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The formalism and model introduced in a previous paper [1984,Molec. Phys.,51,253] and used there to study the inhomogeneous association reactionA+B⇌ABis used here to consider the homogeneous association reaction 2A⇌A2. Two approximations are introduced to obtain an analytic theory. The first is the Percus-Yevick approximation. The second is the neglect of rigid polygonaln-mers,n⩾ 3. (These are sterically possible in our model, but can be expected in most cases to form only rarely because of their restricted geometry.) Representative quantitative results for association probabilities, association constants and radial distribution functions as functions of thermodynamic state are given and discussed. Our model has a dimension-less association parameter τ that is a combined measure of association strength and temperature; for a given atomic number density ρAthere is a value of τ at which diatomic association is complete. Under the assumptions of our theory one then has a fluid of homonuclear diatomics, the hard dumbell fluid. It is found that in this case our theory reduces to the zero pole approximation of Morriss and Cummings for this fluid.

ISSN:0026-8976    

DOI:10.1080/00268978500101141

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

N.M.R. relaxation times of the protons in 18-crown-6 ether have been measured as function of proton density in mixture with the perdeuterated crown ether, of the frequency and temperature. Intramolecular and intermolecular contributions to the relaxation were obtained. Some deuteron relaxation times and spin-echo self-diffusion constants were measured in addition.

ISSN:0026-8976    

DOI:10.1080/00268978500101151

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The effect of the overlapping sphere modification of the muffin-tin SCF-Xα-SW scheme on the potential energy curve of N++2is discussed. Overlapping spheres are used whereby the atomic sphere radii are uniformly increased by 30 per cent with respect to the tangent sphere situation. This procedure which has previously been shown to be successful in predicting equilibrium bond lengths for ground-state molecules, now for the doubly ionized N2molecule results in a potential energy curve in fair agreement with other published data. In particular the so-obtained potential energy curve shows a distinct minimum, whereas the uncorrected muffin-tin scheme gives rise to a repulsive potential energy curve.

ISSN:0026-8976    

DOI:10.1080/00268978500101161

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

In this paper we present molecular dynamics (MD) results for a fluid ofpolarizableLennard-Jones particles with permanent dipole and quadrupole moments. Detailed comparisons are made with theoretical results obtained using a previously developed self-consistent mean field (SCMF) approximation together with the LHNC and QHNC integral equation theories. The SCMF approximation is found to give a reasonably accurate description of the polarizable system. The SCMF/QHNC and SCMF/LHNC calculations both give values for the dielectric constant and average dipole moment which are in good agreement with the MD simulations. The SCMF/QHNC theory gives better results for the pair correlation function and for some thermodynamic properties.

ISSN:0026-8976    

DOI:10.1080/00268978500101171

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The E.S.R. line shape of triplet excitons moving in a coupled coherent and incoherent manner within a pair of differently oriented molecules is calculated numerically. The model hamiltonian contains the electronic interaction matrix element describing the coherent motion within the pair, the Zeeman energy and the fine-structure terms at the two differently oriented molecules. The interaction with vibrations of the crystal is treated microscopically. Considering the phonons as a heat bath with this hamiltonian the Liouville equation for the reduced density operator describing dynamically excitonic and spin degrees of freedom is derived. The eigensolutions of the Liouville equation are determined numerically for parameter values characteristic for naphthalene pairs. Using these eigensolutions the E.S.R. line shape is calculated and finally the connection to experiments is discussed.

ISSN:0026-8976    

DOI:10.1080/00268978500101181

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The dielectric constant and the correlation function of a system of sticky hard spheres with an embedded point dipole is calculated at different densities, temperatures and dipole moments using the LHNC and LIN approximations. Comparison between these theories and with the dielectric constant of hard dipolar spheres are presented. It is found that LIN values are lower than LHNC ones and that the theories predict opposite trends for the dielectric constant when the stickiness is included. An analysis of this discrepancy is given.

ISSN:0026-8976    

DOI:10.1080/00268978500101191

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

E.P.R. studies of Cu2+ion in Cd(NH4)2(SO4)2. 6H2O crystals at 300 K and 77 K showed that the impurity ion has entered the substitutional Cd2+site. The spin hamiltoniangandAparameters and their direction cosines have been evaluated from the observed E.P.R. data. The evaluated parameters are found to have rhombic symmetry. The covalancy parameter (α′2), admixture coefficients (α and β) and fermi-contact term (K) are evaluated using the principalgandAvalues. The ground state wave function for the Cu2+ion is constructed and also the exact signs were assigned for the hyperfine coupling constants (Axx,AyyandAzz). The covalancy indicated the percentage of unpaired spin density present in the metal (Cu2+)d-orbitals. The nature of the distortion present in the lattice is found from the values of themixing coefficients.

ISSN:0026-8976    

DOI:10.1080/00268978500101201

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Pressure dependence of the35Cl Nuclear Quadrupole Resonances (N.Q.R.) in 2,5-, 2,6- and 3,5-dichlorophenols (DCP) has been studied up to a pressure of about 6·5 kbar at room temperature. While the pressure dependence of the two resonance lines in 2,6-DCP is essentially similar, the lower frequency line in 2,5-DCP is almost pressure independent and the higher frequency line shows a linear variation with pressure upto about 3·5 kbar but shows a negative pressure coefficient beyond this pressure. The two lines in 3,5-DCP have a non-linear pressure dependence with the curvature changing smoothly with pressure. The pressure coefficient for both lines becomes negative beyond a pressure of 5 kbar. The pressure dependence of the N.Q.R. frequencies is discussed in relation to intra- and inter-molecular contacts. Also, a thermodynamic analysis of the data is carried out to determine the constant volume temperature derivative of the N.Q.R. frequency.

ISSN:0026-8976    

DOI:10.1080/00268978500101211

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor