Vibron model

From the above discussion, we can see that the purpose of this paper is to present a microscopic model that can analyze the absorption spectra, describe internal conversion, photoinduced ET, and energy transfer in the ps and sub-ps range, and construct the fs time-resolved profiles or spectra, as well as other fs time-resolved experiments. We shall show that in the sub-ps range, the system is best described by the Hamiltonian with various electronic interactions, because when the timescale is ultrashort, all the rate constants lose their meaning. Needless to say, the microscopic approach presented in this paper can be used for other ultrafast phenomena of complicated systems. In particular, we will show how one can prepare a vibronic model based on the adiabatic approximation and show how the spectroscopic properties are mapped onto the resulting model Hamiltonian. We will also show how the resulting model Hamiltonian can be used, with time-resolved spectroscopic data, to obtain internal... 

In order to determine the physical mechanism of initial ET including other rapid kinetics in photosynthetic RCs, it is necessary to construct a vibronic model that comprises the electronic and vibrational states of the system. It is also important to take into account temperature effect in both experiments and theories. In particular, we should stress that most of MO calculations carried out for RCs are based on the crystallographic structures. However, the structure at room temperature may be different from that obtained from the X-ray analysis,... 

Iachello, F., Manini, N., and Oss, S. (1992), Quasi-linear Four-Atomic Molecules in the Vibron Model, 7. Mol. Spectrosc. 156, 190. 

Iachello, F., Oss, S., and Viola, L. (1993a), Vibrational Analysis of Monofluoroacetylene (HCCF) in the Vibron Model, Mol. Phys. 78, 545. 

Lemus, R., Leviatan, A., and Frank, A. (1992), Potential Energy Curves in the Electron-Vibron Model, Chem. Phys. Lett. 194, 327. 

Leviatan, A. (1989), Point Groups in the Vibron Model, J. Chem. Phys. 91,1706. 

General Discussion—Inclusion of Solvent Effects in a Vibronic Model for Mixed-Valence Compounds... 

Vetter and Schulze, charge transfer, 923 Vibrational entropy, 914,915 Vibrational motion of adsorbed ions, 928 Vibron model, 1517... 

We discuss here two examples of vibronic effects in polynuclear highly symmetrical transition metal clusters. The existence of degenerate and quasi-degenerate molecular orbitals in their energy spectra results in the Jahn-Teller effect or in the vibronic mixing of different electronic states. We show that both quantum-chemical methods and model approaches can provide valuable information about these vibronic effects. In the case of the hexanuclear rhenium tri-anion, the Jahn-Teller effect is responsible for the experimentally observed tetragonal distortion of the cluster. The vibronic model of mixed-valence compounds allows to explain the nature of a transient in the photo-catalytic reaction of the decatungstate cluster. 

From the work of O Brien [7] we infer that it should be possible to simulate the EPR spectra of CaO Cu2+ using a single-mode vibronic model, but in doing so the values for the parameters should be regarded as effective quantities. 

Calculations of the level spectra of Ra isotopes using the Vibron model [7] were performed [18]. In these calculations only one parameter was varied between the different isotopes of radium and the results are shown in Fig. 6. The good fits obtained suggest that the cluster model can reproduce the available data of heavy nuclei. 

I would like to acknowledge discussions with D.A. Bromley, F. Iachello and J.F. Shriner, and. the cooperation of M. Ruscev, J.F. Ennis and P.D. Cottle, who worked on °0, °Ra and °Ra respectively, and of H.J. Daley, who worked on the Vibron model code. I also wish to thank R. Bonito and 5. Sicignano for preparation of the camera-ready manuscript. This work was supported in part by U.S. Department of Energy Contract DE-AC02-76ER03074. 

Let s start from the simplest case. The single-level electron-vibron model is described by the Hamiltonian... 

In accord with an approach originally outlined by Jortner and coworkers,41 42 the influence of changing AG° upon the 180 KIE has been modeled using a saddle point approximation.43 At this stage, the experimental variations in 180 KIEs for reactions of O2 and O2" are yet to be determined. The vibronic model of Hammes-Schiffer, which has been used to model proton-coupled electron transfer in accord with a Bom-Oppenheimer separation of timescales, may also be applicable here.44 The objective is to account for the change in 0—0 vibrational frequency together with potential contributions from overlap of vibrationally excited states. The overlap factors involving these states are expected to become more important as AG° deviates from 0 kcal mol 1,39... 

The importance of the vibron model lies in the fact that it is the doorway state of the optical absorption. (The two-particle states have no oscillator strength, since we cannot create vibrations in the ground state.) Indeed, the creation of vibrations is subsequent to an electronic excitation of a molecule, in the approximation where the absorbing dipole is the sum of molecular dipoles (with the appropriate phase), which is the approximation of weak intermolecular forces. 

The positions of the vibronic line, reported in Section II.B.3.a above, allow us to situate the 0-0 center of gravity at Egg = 25279 cm- which is 40 cm-1 below the a component the 392 0-1 vibron provides the same value, Egg 25 280 cm 1. This remarkable coincidence reinforces our confidence in the vibron model of Section II.B. 1. b. 

At low temperatures, narrower bands with better resolution are expected, and the vibronic model predicts lower intensities as well. The polarized spectra at liquid helium temperatures confirm these predictions. Thus, shoulders at 24,000 cm"1 and in the region of 17,000-19,000 cm"1... 

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