摘要:

An account of recent theoretical and experimental advances in the field of excitation transport in disordered systems is presented. First the problem of excitation transport among chromophores (donors) randomly distributed in solution is discussed. Picosecond fluorescence mixing experiments demonstrate that the recent nonperturbative theory for this type of system is accurate at all times and concentrations examined. Next we consider systems with two types of chromophores, donors and traps, randomly distributed in solution. Experiments and theory describe the transport and trapping of excitations over the full range of donor and trap concentrations. These ideas and picosecond transient grating experiments are used to explain the mechanism for fluorescence quenching in concentrated dye solutions, which is shown to be due to excitation transport and trapping by dimers of dye molecules. Finally, the problems of excitation transfer among molecules randomly distributed on a lattice (rather than in a solution) is discussed. An accurate nonperturbative theory is employed to calculate transport observables.

ISSN:0144-235X    

DOI:10.1080/01442358509353360

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

This paper discusses the development of laser Stark spectroscopy (or laser electric resonance spectroscopy) in which transitions between molecular energy levels are tuned into resonance with fixed frequency molecular gas lasers. Emphasis is laid on the fundamentals of the method, and its extensions to sub-Doppler resolution, including optical-optical double resonance and level crossing. Examples of the use of these methods are chosen from three main areas; the study of the vibrational dependence of molecular dipole moments, the elucidation of the effects of collisional energy transfer, and the detection of the spectra of semi-stable molecules.

ISSN:0144-235X    

DOI:10.1080/01442358509353361

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Radiolysis of liquid hydrocarbons produces radical cations and electrons. Their recombination releases sufficient energy in the solvent, or in the solute if a charge scavenger is added, to produce excited states, Because of the low dielectric constant, most of the recombination isgeminate, i.e. the positive and negative charges do not separate as far as the Onsager escape distance (1∼30nm for an alkane at room temperature). For a single ion pair, this means that the two unpaired electrons were initially paired in a molecular singlet state. If recombination is very fast (< 1-10ns), the spin correlation is retained: only singlet products will result. Over longer periods, the correlation decays because of hyperfine interaction between the electrons and magnetic nuclei. This leads to time-dependent magnetic field and magnetic isotope effects on the product yields, easily detected by studying the fluorescence in suitable systems. Spin relaxation randomizes spin orientations but the hyperfine effect is a coherent process and oscillations can be detected. Theory and experiment are in good agreement in most respects. Electron spins can be reversed by absorption of microwaves: the changes in fluorescence can be used for spectroscopic studies of the ions.

ISSN:0144-235X    

DOI:10.1080/01442358509353362

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

ISSN:0144-235X    

DOI:10.1080/01442358509353363

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor