Hannover 2013 – wissenschaftliches Programm
MO 7.4: Vortrag
Montag, 18. März 2013, 17:15–17:30, F 102
How to probe (photo)chemistry in the infrared beyond the vibrational lifetime - Electronically-enhanced 2D-IR exchange spectroscopy used as structural probe — •Luuk van Wilderen, Andreas Messmer, and Jens Bredenbeck — Institute of Biophysics, Goethe-University, Frankfurt am Main, Germany
Conventional 2D-infrared spectroscopy (2D-IR) is limited to probing dynamics on the time scale of the vibrational lifetime, which typically is on the order of a few picoseconds. Processes extending beyond that time so far remained inaccessible. However, many important structural phenomena (e.g. conformational transitions, intermolecular interactions, reactions) can occur in this regime. Here we present a new mixed IR/VIS pulse sequence that allows for the measurement of such processes by means of storing information on vibrational excitation in an electronically excited state. This novel method employs double excitation by a resonant, narrow, tunable infrared pulse and an off-resonant visible pulse, followed by infrared detection. The visible pulse only becomes resonant after vibrational excitation, making the vibrational excitation a prerequisite for entering the electronically excited state. Therefore, the information that vibrational excitation occurred is stored in the electronic excitation and the 2D-IR signal of the vibrational ground state (providing structural molecular information) persists with the electronic lifetime, which can dramatically increase the observation time for exchange phenomena. We illustrate the method by measurements on a mixture of free and hydrogen bonded molecules.