摘要:

The existence of a special type of bound state supported by chemical forces of a different nature from those involved in traditional chemical bonds has been predicted by theory and confirmed by experiment. It is, however, only in the last decade or so that Van der Waals complexes have acquired great relevance as model systems for the study of energy flow and energy deposition during intramolecular inelastic processes. In the present analysis it is shown how even the simple event where energy is exchanged only between internal rotation and the vibrational motion along the Van der Waals (VdW) bond can lend itself to a very detailed and systematic study of the origin of the dominant dynamical couplings which drive the inelastic rearrangements. A computational example is given at the end for the case of argon and molecular nitrogen, as partners moving under the effect of a realistic interaction potential determined from several experimental data.

ISSN:0144-235X    

DOI:10.1080/01442358809353203

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The relaxation processes responsible for the finite lifetime of excited vibrational states in molecular crystals are discussed on the basis of recent experimental and theoretical developments. Experimental information on the lifetime of optically active phonons is obtained in the time domain by time-resolved CARS spectroscopy or in the frequency domain by high-resolution infrared and Raman spectroscopy. The experimental results are then interpreted in terms of many-body perturbation techniques or of molecular dynamics simulation.

ISSN:0144-235X    

DOI:10.1080/01442358809353204

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

In the spin-coupled description of molecular electronic structure, an N-electron system is described byNdistinct—but non-orthogonal—orbitals, whose spins are coupled to the required resultantSin all possible ways. The coefficients of the basis functions comprising the orbitals and the coefficients of the different spin functions are fully optimized. The orbitals are frequently highly localized, and hence the model incorporates considerable electron correlation while retaining a high degree of visuality. The spin-coupled wave function is refined by non-orthogonal configuration interaction, and the final wave functions are of high quality but very compact. The various aspects of this theory are illustrated by a series of examples of increasing complexity: the H2molecule, the BeH molecule, the3B1andlA1states of CH2and the cycloaddition of CH2to ethenes, the 7t-electron system of benzene, and diazomethane (CH2N2). The results provide clear descriptions of the electronic structure and the associated processes. In benzene, the six π orbitals are highly localized, with far-reaching implications for the description of aromatic systems. The case of diazomethane shows that the central N atom takes part infiv. electron-pair bonds, and the same is true for a series of molecules such as N2O, Hcno, NO2, and CH2NHO (nitrone), whose structures have long caused problems in valency theory.

ISSN:0144-235X    

DOI:10.1080/01442358809353205

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Some of the methods used in probing the structure and performance of heterogeneous catalysts are discussed. We consider X-ray diffraction, neutron diffraction and neutron inelastic scattering, high-resolution electron microscopy, electron diffraction, electron energy loss spectroscopy, and computational methods. The determination by X-ray diffraction of siting and occupancy of extra-framework cation Ni2+in faujasite or by neutron diffraction of H+in La3+-Y catalyst are discussed. Some of the methods are complementary and a combination of two or more can be used to gain a better understanding of the problem.

ISSN:0144-235X    

DOI:10.1080/01442358809353206

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Advances in Chemica. Physics—Volume 67. Ab Initio Methods in Quantum Chemistry—Part I. Edited by K. P. LAWLEY. (John Wiley and Sons, 1987.) [Pp. 566.] £6500. ISBN 0471909009.

ISSN:0144-235X    

DOI:10.1080/01442358809353207

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor