Excitable dynamics

Spectroscopy and Excitation Dynamics of Condensed Moiecuiar Systems (Modern Probiems in Condensed Matter Sciences 4) eds V M Agranovich and R M Hochstrasser (Amsterdam North-Holland) pp 249-300... 

Fujino, T, and Tahara, T. 2003. femtosecond fluorescence up-conversion microscopy Excitation dynamics in ct-perylene microcrystal. J. Phys. Chem. B 107 5120. 

M. Shmilovits-Ofir, R. B. Gerber. Proton transfer and dissociation of GlyLysH(- -) following O-H and N-H stretching mode excitations dynamics simulations, J. Am. Chem, Soc., 133 ... 

Nonlinear Laser Spectroscopy and Dephasing of Molecules An Experimental and Theoretical Overview, M. J. Bums, W. K. Liu, and A. H. Zewail, in Spectroscopy and Excitation Dynamics of Condensed Molecular Systems, Series in Modem Problems in Condensed Matter Sciences, Vol. 4, V. M. Agranovich and R. M. Hochstrasser, Eds., North-Holland Publishing, Amsterdam, New York, Oxford, 1983, Chapter 7, p. 301. 

Personov RI (1983) In Agranovich VM, Hochstrasser RM (eds) Spectroscopy and excitation dynamics of condensed molecular systems. North Holland, Amsterdam, p 555... 

Excitation Dynamics. The response of atomic and molecular systems to exciting radiation has long been of interest and work has been going on to understand such phenomena for over one hundred years (18). Recent work has involved the use of lasers and modern detection systems to observe and measure individual radiative and collisional rates. 

Hesselink WH, Wiersma DA. Theory and experimental aspects of photon echoes in molecular solids. In Agranowich VM, Hochstrasser RM, eds. Spectroscopy and Excitation Dynamics of Condensed Molecular Systems. North Holland Elsevier Science, 1983 249-299. 

Karapetyan, N.V., Holzwarth, A.R., and Rogner, M. (1999) The photosystem I trimer of cyanobacteria molecular organization, excitation dynamics and physiological significance, FEBSLetters 460, 395-400. 

V. M. Kenkre, in Excitation Dynamics in Molecular Crystal and Aggregates, Springer Tracts in Modern Physics. Vol. 94, Springer, Berlin, 1982, p. 1. 

A typical problem of interest at Los Alamos is the solution of the infrared multiple photon excitation dynamics of sulfur hexafluoride. This very problem has been quite popular in the literature in the past few years. (7) The solution of this problem is modeled by a molecular Hamiltonian which explicitly treats the asymmetric stretch ladder of the molecule coupled implicitly to the other molecular degrees of freedom. (See Fig. 12.) We consider the the first seven vibrational states of the mode of SF (6v ) the octahedral symmetry of the SF molecule makes these vibrational levels degenerate, and coupling between vibrational and rotational motion splits these degeneracies slightly. Furthermore, there is a rotational manifold of states associated with each vibrational level. Even to describe the zeroth-order level states of this molecule is itself a fairly complicated problem. Now if we were to include collisions in our model of multiple photon excitation of SF, e wou d have to solve a matrix Bloch equation with a minimum of 84 x 84 elements. Clearly such a problem is beyond our current abilities, so in fact we neglect collisional effects in order to stay with a Schrodinger picture of the excitation dynamics. 

Figure 12. Schematic of multiple photon excitation dynamics of SFe. Groups of levels show lowest three vs vibrational states. Higher states are split by rotational interactions with vibrational motion.

Figure 16.5 shows the possible relaxation pathways of excited organic molecules following absorption of photons. Elementary excitation dynamics, including generation, relaxation and deactivation are considered here, which are similar to those occurring in most optoelectronic devices. 

Another important effect due to the spin-orbit coupling comes into play whether the upper ionic core is specifically involved or not. This is because the excitation dynamics is very sensitive not only to the ionization potential or binding energy of the active electron but also to m, the projection of the orbital angular momentum along the polarization axis. Since spin-orbit terms are not... 

This completes our brief description of the computational methods used in these studies. In the following sections some recent results will be presented and discussed. We will cover the calculation of ionization rates, the photoelectron energy distributions, the determination of the residual excited state populations remaining after excitation by a short pulse and finally show some photoemission spectra. The shape of the pulse envelope clearly can affect all these observable quantities. For example, the final state populations are found to be very sensitive to the pulse width and the peak intensity. Such results emphasize the point that in a strong, short pulsed field, the time dependence of the field envelope is reflected in the time evolution of the excitation dynamics. During the pulse. 

The future of this field clearly will rely on extending these, or some other, methods to study two-electron systems and simple molecular systems. There is evidence that electron-electron correlation continues to play a role in excitation dynamics even in very intense fields. The interaction can be small, but it has been observed to yield orders of magnitude enhancements in the production of doubly charged ions for intensities below that at which sequential ionization becomes efficient. In molecules, the transfer of absorbed energy from the electrons to the nuclei which controls the competition between ionization and dissociation is another important and developing field of research. 

The Parlser-Parr-Pople (PPP) model for ir-electrons Is extended to polydlacetylene (PDA) excitations. Dynamic Coulomb correlations between the two v systems o the PDA triple bonds lower and split the excltonlc 1 6 absorption In short segments. Such coupling occurs In correlated states of ene-yne molecules, qualitatively changes their low-lying excited states, and admixes pseudocovalent valence-bond (VB) structures describing simultaneous transfers In both ir systems. 

It is clear from our results that the initial excitation in solid polystyrene must be extremely mobile in contrast to the case of the polymer in solution. However, it is now clear that available experimental results do not directly examine the mobile excitation. In particular, observed "monomer-like" emission is due to a shallow trap, which vitiates a previous analysis (Id,18) that assumed it to be due to the mobile excitation. Direct determination of mobile excitation dynamics will require extension of photophysical measurements to the picosecond time regime and efforts by us to accomplish this goal are now in progress. 

Exciton coherence. Payer, M.D.in Spectroscopy and Excitation Dynamics of Condensed Molecular Systems. Agranovich,V.M. Hochstrasser, R.M. Eds. North-Holland Amsterdam, 1983, p.l85. 

A considerable number of papers deal with the details of specific systems. Only a selection of these can be mentioned these are ground state anion formation and ps excitation dynamics of 3-hydroxyflavone in formamide " styrylphenanthrene-... 

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