Max Planck Institute for Dynamics and Self-Organization -- Department for Nonlinear Dynamics and Network Dynamics Group
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Sonderseminar

Tuesday, 19.10.2010 11 c.t.

Chiralsensitive Spectroscopy in the Liquid-Phase

by Andreas Steinbacher
from Universität Würzburg

Contact person: Marc Timme

Location

Seminarraum Haus 2, 4. Stock (Bunsenstr.)

Abstract

A precise and rapid polarimeter based on the common-path optical heterodyne interferometry method is presented [1, 2]. The femtosecond pump and polarimeter probe beams are integrated into the recently developed accumulative technique for femtosecond spectroscopy [3]. The optical rotation of the liquid sample volume is translated into a phase retardation of the probe beam. This allows accumulation of achiral photoproducts to increase the optical rotation change while conserving the femtosecond time resolution, as demonstrated for the photodestruction of methyl p-tolyl sulfoxide enantiomers. The high speed of the polarimeter affords optical rotation detection during the illumination period of a few seconds, to follow the outcome of the photochemical reaction on-line. The absorption spectrum at 275􀀀400 nm of the same sample volume is recorded at the same time to observe the very weak absorption increase due to product formation of the photodestruction. Both detection methods, linear absorption and optical rotation, reveal a chemical reaction of the enantiomers, with the phase-sensitive detection method of the polarimeter being far superior in contrast. Furthermore, the polarimeter probe, in contrast to the linear absorption probe, is also able to distinguish between enantiomers [4]. While theoretical calculations predict possible accuracies of better than 3:5 _ 10􀀀5 _, our measurements achieved a true resolution of 1:2 _ 10􀀀4 _, for a measurement time of only one second and an interaction length of only 250 µm.

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