摘要:

In this paper we present a derivation of the rotational line strengths involved in fully resonant degenerate four wave mixing processes (DFWM). General expressions are given for diatomic molecules with different Hund's coupling cases. More precisely, we tabulated the rotational line strengths for the electronic transition2Σ+-2Π of OH and NO. For the ground state, Hund's cases (b), (a) and the intermediate case (a-b) are considered. We also stress the dependence of the line strengths with respect to the geometry and to the polarization of the incident beams. So, we consider the optical phase conjugation (OPC) geometry and the forward (FDFWM) one. We also give expressions for the line strengths in different polarization arrangements, i.e. parallel or crossed polarized beams. A comparison is made between these cases. Finally, theoretical simulations, using our line strengths calculations, are compared with experimental spectra of OH obtained in a methane-air flame using OPC and FDFWM.

ISSN:0026-8976    

DOI:10.1080/00268979300101731

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The rotational part contains the angular velocity ω and the modified moment of inertia tensorI' of Wilson and Howard, which also occurs in the relationJα- πα= ΣβI'αβωβinvolving the total (J) and vibrational (π) angular momenta. In case (i),I′ has a vanishing z row and column, wherezis the axis of the molecule. This is associated with the Sayvetz condition that the total angular momentum about the axis is purely vibrational. These equations therefore contain only the two components ωxand ωyof ω, which can be eliminated to give the Hamiltonian form of the kinetic energy. In case (ii), thezrow and column of theI' matrix are non-vanishing andI' is non-singular. The three components of ω can therefore be obtained in terms of the angular momenta, to give a treatment that is entirely analogous to that for a nonlinear reference configuration. The parameters of the case (ii) Hamiltonian are expressed in terms of those of case (i).

ISSN:0026-8976    

DOI:10.1080/00268979300101741

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A novel product operator formalism for strongly coupled two-spin systems was developed which allows the time evolution for such systems to be estimated much more easily than using the density matrix. The newly developed theory was applied to describe the INADEQUATE (Incredible Natural Abundance DoublE QUAntum Transfer Experiment) experiments, and the condition for the efficiency of the creation of the double-quantum coherences was formulated, which is useful for setting the experimental conditions. The refocused INADEQUATE spectra of benzyl bromide, in which two one-bond13C—13C pairs have extremely strong couplings compared with the chemical shift differences, were observed under several experimental conditions. The signals attributable to these strongly coupled spin pairs were detected with reasonably large intensities, and their coupling constants were determined by simulation of the spectral intensities; the weak and the long-range couplings in the compound were also obtained.

ISSN:0026-8976    

DOI:10.1080/00268979300101761

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Potential energy curves for the triplet states of the ionic excimer Ar22+are computed in an all-electron treatment employing multireference configuration interaction (MRD-CI) calculations. The six states3Σ+u(2),3Πg,3Πu,3Δuand3Σ-gdissociating into Ar+(2Pu) + Ar+(2Pu) are confirmed to be repulsive, while the four triplets3Πg,3Πu,3Σ-gand3Σ-udissociating into Ar2+(3Pg) + Ar(1Sg) are computed to be weakly bound possessing equilibrium distances between 5·6 and 6·0 bohr and dissociation energies in the range of 2450–3180 cm-1. According to the calculation, the strongest bound-free emission occurs fromv′ = 0 of the 23Πgstate at 182 nm followed by the 23Πu-3Πgtransition at 181·8 nm and de-excitation from the3Σ-ustate around 168 nm; it is unambiguously assigned to the first maximum measured around 183 nm in the third continuum of the argon excimer spectrum. The calculated radiative lifetime of 6 ns (compared with the measured value of 5 ns) also supports this assignment.

ISSN:0026-8976    

DOI:10.1080/00268979300101771

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The electronic structures, optimized geometries and harmonic vibrational frequencies of F-3, Cl-3, F3and Cl3have been studied byab initiocalculations, using various basis sets and different correlation methods, including MP2, CISD and CASSCF. For the anions, reasonably consistent results were obtained for the closed-shell singlet ground states. However, for the open-shell doublet states of the neutral trihalogens and the triplet states of the anions the optimized geometries and hence the computed harmonic vibrational frequencies were found to be rather basis set and method dependent. Calculations based on a single configuration are inadequate for the neutral trihalogens, and the electronic structures of the various open-shell states of both the neutral trihalogens and their anions are rather complex. The different effects due to basis set size and dynamic and non-dynamic electron correlation on the various electronic structures, optimized geometries and computed harmonic vibrational frequencies obtained are discussed. Comparison with experimental data was made where available.

ISSN:0026-8976    

DOI:10.1080/00268979300101781

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Percus-Yevick (PY), hypernetted chain (HNC) and modified Verlet (VM) integral equation theories are used to study the structure and thermodynamic properties of hard prolate ellipsoids of revolution in the isotropic fluid region. Results for the spherical harmonic coefficients of the pair distribution function and for the compressibility factors are compared with new Monte Carlo results reported in this work for length-to-breadth ratiosa/b= 2, 3, and 5. Fora/b= 2 and 3, the VM harmonic coefficients are in good agreement with the simulation results and are better than those of PY and HNC theories. Fora/b= 5, HNC theory gives numerically precise harmonic coefficients, the VM results being only slightly inferior, a behaviour consistent with that found previously for very long spherocylinders. VM theory gives equation of state results in excellent agreement with the simulation data at all values ofa/band densities, whereas the PY and HNC results are generally poor. The thermodynamic consistency of each of the PY, HNC and VM theories is tested by comparing the compressibility factors calculated from the pressure and compressibility equations. A recently derived formula for the chemical potential is used as another consistency test of the theories. At all state points considered, the consistency of VM theory is excellent and much better than that of PY and HNC theories. The orientational spinodal density ηsof the isotropic fluid phase was estimated by extrapolating the inverse Kerr constant to zero. We find that VM theory gives values of ηsthat are higher than the HNC values and lower than the PY values. The correct values of ηslikely lie between the HNC and VM results.

ISSN:0026-8976    

DOI:10.1080/00268979300101791

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Calculations of the elastic constants and lattice vibrations of CO2and C6H6have been carried out, using the harmonic lattice dynamic procedures available in the THBREL and THBPHON programs. In addition to the usual Buckingham functions describing the non-bonded interactions, intramolecular potentials are also employed. Two sets of calculations were performed, the first for rigid molecules and the second for flexible molecular units, with a view to assessing the effect of molecular flexibility on the computed values of the elastic tensor components and lattice vibration frequencies. The results are also compared with those of previous studies, using methods in which the rigid-body contributions are clearly isolated, and with available experimental data.

ISSN:0026-8976    

DOI:10.1080/00268979300101801

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The structures of the three phases of DBr and DI were determined using neutron powder profile techniques. The highest temperature phases are cubic, Fm3m, with the deuteriums in twelvefold disordered positions about the halogens. The intermediate temperature phases are orthorhombic, Cmca, with the deuteriums in twofold disordered positions about the halogens in the mirror planes. In the lowest temperature phase of DBr, molecular ordering results in zigzag chains of molecules in the mirror planes of an orthorhombic structure with space group Cmc21. Molecular ordering appears in a different way in DI giving distorted diamonds (almost squares), rather than chains, and the rotational sense within the diamonds differs from one plane to the next. DI molecules are parallel or perpendicular to each other but the molecules point 6·27° away from the lines joining the iodines. the structure is triclinic, with space group P1.

ISSN:0026-8976    

DOI:10.1080/00268979300101811

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We report the synthesis of a new triradical material: 1,3,5,-tri-6′-(1,3,5,-tri-phenylverdazyl)-benzene. It is characterized by1H-NMR in solution, static magnetic susceptibility measurement and EPR (electron paramagnetic resonance) in crystalline solid state and dilute liquid as well as frozen solution. Hyperfine coupling and fine structure splitting are analysed. In the solid state, the spin-quartet state is situated at ΔEQ-D/kB= 20K above the doublet ground-state. EPR-line exchange narrowing indicates substantial intermolecular exchange interaction. Ferromagnetic and antiferromagnetic exchange interactions cancel in the crystalline solid, however. We point to the influence of the molecular packing in the solid state on the molecular magnetic properties (doublet-quartet separation).

ISSN:0026-8976    

DOI:10.1080/00268979300101821

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

By making use of recently obtained theoretical and Monte Carlo simulation results for solid state thermodynamics and solid-fluid equilibria for systems of hard dumbbells a generalized van der Waals theory of solid-fluid equilibria has been formulated. The theory predicts how the temperature dependence of the solid-liquid (and vapour-liquid) equilibrium is influenced by non-spherical molecular shape for diatomic molecules. Two regimes of behaviour are identified, depending on whether the underlying hard dumbbell reference system freezes into a plastic crystal or an orientationally ordered crystal. The theory correctly predicts a decrease in the triple point temperature and density change on freezing between spherical molecules, such as argon, and slightly non-spherical molecules which freeze into plastic crystal phases such as nitrogen. An extension of the theory which includes a simplified treatment of the influence of quadrupolar interactions provides a plausible explanation for the relatively high reduced triple point temperature of carbon dioxide.

ISSN:0026-8976    

DOI:10.1080/00268979300101831

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor