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AG Zinth - Projects
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The flow of vibrational energy in molecules (Femtochemistry - Femtobiology) The flow of vibrational energy within a molecule and between a molecule and its solvent surrounding is of crucial importance for chemical dynamics. This flow on the one hand transports energy from the bath modes to the reactive vibrational modes and thereby initiates the reaction. On the other hand it also stabilizes the reaction products by distributing the reaction energy among intra- und intermolecular bath modes. Since these energy redistributions occur on the subpicosecond to picosecond timescale, ultrafast techniques are required to study them. In our lab we employ time resolved emission methods to monitor transient vibrational excitations. Three types of experiments were performed: 1. IR-excitation A vibrational mode of a polyatomic molecule is excited with a short (~ 100 fs) IR laser pulse. The vibrational excitation is monitored via anti-Stokes-Raman scattering. This allows to determine timescales and pathways of the vibrational relaxation in the electronic ground state. 2. Optical excitation By electronic excitation with an optical femtosecond laser pulse a photophysical or photochemical process is triggered. The vibrational excitation of the products of this process is detected via probe pulse induced anti-Stokes emission. The method could for example successfully be employed to monitor the cooling of the photofragments of the photodissociation of triiodide. Currently the applicabiliy of this method for the study of larger molecules is tested. 3. Optical excitation, IR-probe Infrared spectroscopy, more preciously time-resolved visible pump-/infrared probe spectroscopy, is a complementary method the one, which was described in the previous section. Electronic excitation is done by a visible femtosecond pulse (~100 fs). Vibrational modes are followed by equally short pulses in the infrared range of 1000-3000 cm-1.
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