摘要:

Two-state small-polaron models commonly used to describe an electron donor—acceptor pair are reviewed. From such models, one obtains a one-dimensional model potential. In the homonuclear case, the reaction coordinate for the potential is an antisymmetric vibrational mode. Four situations are discussed in which the two-state small-polaron models break down. Frequency shifts in a nuclear mode upon addition of an electron correspond to vibronic coupling terms in the Hamiltonian which are quadratic in the nuclear coordinate. These quadratic coupling terms lead to the coupling of a totally symmetric mode. Similarly, when an additional electron state is coupled to the donor and acceptor orbitals, at least one additional (totally symmetric) mode becomes coupled to the electronic motion. If the Condon approximation is not invoked, the donor—acceptor distance coordinate becomes coupled to the electronic transition also. The same type of behaviour in the potential occurs when the electron donor—acceptor couple is subjected to an external electric field. Implications for the optical absorption line shapes and rates of electron transfer, which can be qualitatively different from the predictions of the two-state small-polaron model, are discussed.

ISSN:0144-235X    

DOI:10.1080/01442359509353302

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Methods for the analysis of highly excited vibrational eigenstates are presented. These include semiclassical and hierarchical analyses, along with a discussion of the nature of eigenstates along a correlation diagram. The purpose of the analyses is to extract information from what often appear to be complicated, ‘unassignable’ eigenstates. In particular, I address how to rationalize the nature of eigenstates via the semiclassical analysis and how to extract information concerning assignability and energy flow from the hierarchical analysis. The study of the eigenstates along a correlation diagram, together with the semiclassical analysis, is undertaken to address the issue of the classical-quantum correspondence when the classical mechanics is chaotic.

ISSN:0144-235X    

DOI:10.1080/01442359509353303

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Multiphoton ionization spectroscopy is a tool for the elucidation of the structure of high-energy states of atoms and molecules. Particularly when used in combination with time-of-flight mass spectrometry and photoelectron spectroscopy, the range of applications include pure spectroscopic studies, the quantum state specific detection of reactants and products and the preparation of quantumstate-selected reactants for chemical reactivity studies. As such, the techniques have become ubiquitous in the field of chemical reaction dynamics. This paper is concerned mainly with the describing the range of these applications and techniques and a selection of typical results.

ISSN:0144-235X    

DOI:10.1080/01442359509353304

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Quantum Monte Carlo methods cannot at present provide exact solutions of the Schrödinger equation for systems with more than a few electrons. But, quantum Monte Carlo calculations can provide very low energy, highly accurate solutions for many systems ranging up to several hundred electrons. These systems include atoms such as Be and Fe, molecules such as H2O, CH4, and HF, and condensed materials such as solid N2and solid silicon. The quantum Monte Carlo predictions of their energies and structures may not be ‘exact’, but they are the best available. Most of the Monte Carlo calculations for these systems have been carried out using approximately correct fixed nodal hypersurfaces and they have come to be known as ‘fixed-node quantum Monte Carlo’ calculations. In this paper we review these ‘fixed node’ calculations and the accuracies they yield.

ISSN:0144-235X    

DOI:10.1080/01442359509353305

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

External electric fields can halt the rotation of polar molecules and produce pendular states in which the molecular dipole μ is confined to librate over a limited angular range about the space-fixed direction of the external field. The pendular eigenfunctions are hybrids of field-free rotor states, (J,K,M) with indefinite (forK≠ 0) or alternating (forK= 0) parities; this renders the parity of the hybrid wavefunctions indefinite for any values of the good quantum numbersKorM. As a result, the parity selection rule for the matrix elements of tensor operators in the pendular basis, notably the electric dipole moment, is lifted. We give the expectation values of the space-fixed dipole moment operator and of the orientation cosine of the figure axis and illustrate the lifting with field strength of the parity selection rule for prototype hybrid states of polar molecules. The symmetry properties of the pendular Hamiltonian are used to sort the eigenstates according to the sign of the product ofK, M, and μ.

ISSN:0144-235X    

DOI:10.1080/01442359509353306

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Ab initiocomputations have been carried out during the past several years on diamides of single amino acids (HCO-NHCHR-CONH2whereR=H (glycine), -CH3(alanine), -CH(CH3)2(valine) and -CH2OH (serine)) exploring all possible backbone and side chain conformations. Selected conformations were studied in our laboratory on threonine (R=CH(CH3)OH), cystein (R=CH2-SH) and phenyl-alanine (R=CH2-CH5H6) diamides. Tri-, tetra-, penta-, hexa- and hepta-amide systems of poly-L-alanine (H-(CONH-CHCH3-CONH)n-H 2⩽n⩽6) were also investigated at selected backbone conformations. All these studies confirmed the results of multidimensional conformation analyses: thejth amino acid residue in a polypeptide has a maximum of nine (9) discrete backbone conformations. These structures correspond to nine conformational centres on the 2D-Ramachandran map. On the basis of this rinding, it can be shown that the folded secondary structure of any protein with known internal coordinates, can be described in terms of these nine discrete conformation types.

ISSN:0144-235X    

DOI:10.1080/01442359509353307

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor