摘要:

The simultaneous translational and rotational brownian motions of an assembly of interacting cylindrically symmetric polar molecules are assumed to obey a generalizedN-particle Smoluchowski-Einstein-Debye equation. Rigorous relations are derived between the self-rotational diffusion coefficient and the initial slopes of the pertinent orientation correlation functions for both dielectric relaxation and depolarized dynamic light scattering. These exact results are obtained by an appropriate generalization of the rigorous treatment of Ackerson for the initial slope of the normalized dynamic structure factor of an assembly of interacting spherically symmetric translational diffusers.

ISSN:0026-8976    

DOI:10.1080/00268978000102121

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Molecular dynamics (MD) simulations of an isolated dipolar system (made of Stockmayer molecules) has been performed. A two dimensional system has been adopted, using a ‘2-D electrostatics’ dipolar interaction.

ISSN:0026-8976    

DOI:10.1080/00268978000102131

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

We present a study, using the brownian dynamics simulation technique, of a simple model of a chemical reaction in solution. The model consists of the transfer of a particle between two substrate species in a reaction complex which interacts with its surroundings through frictional effects and random force terms. We pay particular attention to the regime in which both the barrier to transfer and the degree of interaction between the transferred particle and its environment are low.

ISSN:0026-8976    

DOI:10.1080/00268978000102141

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The interaction energy of two atoms in the presence of an external electrostatic field is evaluated up to sixth order with the help of covariant field-theoretical perturbation theory. The divergent Feynman diagrams entering the calculation are resummed according to a systematic procedure that has been developed in a previous paper. The pair polarizability and first hyperpolarizability that give the response of the interacting atoms to the external field are subsequently obtained from the energy shift by virtue of a Hellmann-Feynman theorem. The retardation effects showing up in the pair polarizability are discussed in detail.

ISSN:0026-8976    

DOI:10.1080/00268978000102151

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

We show for a model system previously studied by Moiseyevet al.(1978,Molec. Phys.,36,1613) how, with a basis of sufficient flexibility, the wave-function of the complex coordinate method can approach the function which can be directly obtained from a numerical integration of the wave equation with a complex coordinate and a complex energy. Diagrams of the complex wavefunction are used to visualize its behaviour in the short and long range regions, and the attenuation (localization) produced by the rotation.

ISSN:0026-8976    

DOI:10.1080/00268978000102161

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Analytic expressions for the spin responses toPy(90°)-τ-Px(β) andPy(90°)-τ-Py(β) pulse sequences are obtained for a model of two dipolar coupled spins-1 each subject to local electric field gradients. Three distinct echoes with different time dependences are predicted. When ωQ> ωD, these echoes are not resolvable and only a single composite echo att′ = τ will be observed. The amplitude of thePy(90°)-τ-Px(90°) echo as a function of τ corresponds to a time-domain spectrum reflecting the dipolar interaction and the orientational distribution. The applicability of the model to experimental deuterium spin responses in perdeuteriated molecular solids is examined. The β-dependences of the responses and the short time behaviour are accurately reproduced, though, as expected, there are discrepancies at long times. The failure of the time-expansion approach to predict the observed second order decay coefficient for thePy(90°)-τ-Px(90°) echo amplitude is explained; it is also shown that this coefficient will have the value 8/9M2vvfor all materials of practical interest. The distortion of the shape of the echo compared with the FID signal is discussed briefly.

ISSN:0026-8976    

DOI:10.1080/00268978000102171

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The collision induced isotropic and anisotropic spectra of light scattered from fluids of tetrahedral molecules are examined. The interaction function used includes the dipole-induced dipole effect (DID) and the collision induced rotational Raman effect (CIRR) to lowest order. The spectra are expressed as the Fourier transforms of four point correlation functions which contain the number density and the orientational density of the particles. The polarization ratioIVVCIRR(ω)/IVHCIRR(ω) for the CIRR contributions considered is shown to be 37/9 for all densities. The various terms contributing to the integrated intensity for the pair and triplet collisions are expressed in terms of the irreducible expansion coefficients of the orientation dependent pair distribution function. As an example, these terms are evaluated numerically for carbon tetrachloride for two different densities corresponding to a liquid and a vapour state.

ISSN:0026-8976    

DOI:10.1080/00268978000102181

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The response of spin-1 nuclei to sequences of high-power, non-selective r.f. pulses is calculated in detail using the Redfield density matrix formalism and Wigner rotation matrices. The spin system considered is subject to both a large, static Zeeman interaction and a small, first order, secular quadrupole coupling. It is shown that an in-phase pulse pair, 90°x-τ-90°x, applied such that the second pulse occurs at a zero-crossing of the on-resonance free-induction decay signal following the first pulse, creates a state of pure double quantum coherence and is thus equivalent to the soft double-quantum 90° pulse described by Pines and co-workers [6–10, 23]. In addition, in the presence of a resonance offset, Δ, it is shown that this state may be created either by an appropriate choice of Δ or by using the modified pulse sequence, 90°x-τ/2-180°x-τ/2-90°x. The response of the state of double-quantum coherence to resonance offsets and subsequent r.f. pulses is also investigated in some detail. In particular the effect of a general pulse, Θα, applied to the system after the double-quantum coherence has evolved for a period under the influence of a resonance offset, Δ, is calculated and the conditions required to effect total transfer of the order back into transverse magnetization (single-quantum coherence) are evaluated. Similarly, the conditions which effect a transfer of the double-quantum coherence into a mixed state of quadrupole (zero-quantum) and double-quantum order are discussed. The results clearly show the relationships between the phases of the r.f. pulses, the magnetization vectors, and the state of double-quantum coherence necessary to effect these transfers and thus lead naturally to a set of pictorial models for these processes. These involve consideration of both single-quantum and double-quantum frames of reference and agreement between the models and theory is quantitative, even to the derivation of operators corresponding to the cartesian components of the double-quantum coherence vector in the double-quantum frame. These operators are identical to those described by Vega and Pines [9] and Wokaun and Ernst [13].

ISSN:0026-8976    

DOI:10.1080/00268978000102191

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The He(I) photoelectron spectrum of the FO(X2Πi) radical, produced from the rapid reaction

ISSN:0026-8976    

DOI:10.1080/00268978000102201

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Room temperature rotational Raman spectra of N2in the 56–135 amagat density range are employed to test the memory function approach to rotational dynamics. Memory functions of order one and two in the Mori hierarchy are derived from the spectra and compared with the corresponding calculated free rotor memory functions. It is found that the free rotor memory function multiplied by a decaying function approximately reproduces the experimental curves, the degree of approximation being sensibly better for the second order memory function. Exponentially decaying functions are required to reproduce the long time behaviour of both experimental memory functions. At short times a gaussian decay is found to be more adequate for the first order memory function. Decay parameter values are discussed and compared with available theories.

ISSN:0026-8976    

DOI:10.1080/00268978000102211

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor