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Quantum dynamics and solvation effects in clusters and condensed phases


Research objectives and content
We are planning to investigate the dynamics of an Iodine molecule embedded in a cluster or in a low temperature rare gas matrix when excited with an ultrashort laser pulse. This system has been studied experimentally in great detail [1]. In particular, the advent of intense tailored laser pulses has spurred much interest in examining the nonlinear behaviour of molecular systems in intense laser fields and has opened the way to quantum control of intramolecular dynamics in a condensed phase environment [2].
Rigorous quantum treatment of the dynamics can only be done for small clusters. Approximate models have to be developped for larger systems and for the condensed phase. It is possible to study the short-time dynamics of the optically active molecule (the chromophore) by numerically solving the Schrodinger equation, but the coupling with the bath has to be modelled by a hybrid method combining classical and quantum pictures [3]. In the case of iodine, several competing processes are active in the region of the visible spectrum, namely vibrational relaxation, electronic predissociation and the associated cage effect which makes some molecules recombine in a different electronic state. Whether these processes are affected by the formation of transient van-der-Waals complexes or by the average fluctuating molecule-bath interaction, remains to be investigated theoretically very carefully. This investigation is the subject of this research proposal.
[l] Y. Yan, R.M. Whitnell, K.R. Wilson and A. Zewail, Chem. Phys. Lett. 193, 402 (1992) [2] Femtosecond Chemistry, ed. by J. Manz and L. Woste (VCH Heidelberg, 1995) [3] P. Jungwirth, R.B. Gerber, J.Chem.Phys 102, 6046 (1995)
Training content (objective, benefit and expected impact)
The study of clusters composed of an optically active molecule (the chromophore) and many bath atoms or simple molecules is an active area of research which can provide important information on solvent effects and on the transition of atomic properties from isolated species to the condensed phase. With the combined use of supersonic beams and tailored ultrashort laser pulses it is now possible to study in great detail these systems in excited electronic states. Important theoretical work remains to be done in order to interpret and elucidate the underlying dynamics of these systems after excitation with laser pulses. This is of greatest interest with respect to controlling molecular dynamics by light.
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