Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
Department Online Seminar
Chair: Takashi Kumagai

Monday, September 28, 2020, 11:00 am
Prof. Hikaru Kuramochi
Institute for Molecular Science, Japan
Mapping Ultrafast Chemical Reaction Dynamics with Femtosecond Time-Resolved Time-Domain Raman Spectroscopy
In ordinary Raman spectroscopy, the laser source illuminates the sample, and the scattered light is collected, dispersed, and detected by a multi-channel detector yielding a Raman spectrum directly in the frequency domain. On the other hand, it is also possible to obtain a Raman spectrum by observing coherent molecular vibrations directly in the time domain using ultrashort pulses. While it provides the information equivalent to ordinary “frequency-domain” Raman spectroscopy, the uniqueness of time-domain Raman spectroscopy is that, by introducing the femtosecond actinic pump pulse prior to the Raman probing process, it is possible to track structural changes of reaction intermediates occurring on the femtosecond time scale [1]. Based on this idea, we developed a time-resolved “time-domain” Raman spectrometer featuring sub-7-fs pulses, which enables us to track the change of the vibrational structure over a wide frequency range from the terahertz to 3000 cm-1 region, with femtosecond time resolution and exquisite sensitivity down to ~1 mOD [2]. With these capabilities, we succeeded in visualizing ultrafast structural dynamics during not only fundamental chemical processes such as chemical bond dissociation/formation [3,4], but also primary events in the photoreactions of photoresponsive proteins [5-7]. In the talk, we provide an overview of these studies and discuss the potential and future of time-domain Raman spectroscopy.

[1] S. Fujiyoshi, et al, J. Phys. Chem. A 107, 494-500 (2003).
[2] H. Kuramochi et al., Rev. Sci. Instrum. 87, 043107 (2016).
[3] H. Kuramochi et al., Chem. Phys. 512, 88 (2018).
[4] H. Kuramochi et al., J. Am. Chem. Soc. 141, 19296, (2019).
[5] T. Fujisawa, H. Kuramochi et al., J. Am. Chem. Soc. 138, 3942 (2016).
[6] H. Kuramochi et al., Nat. Chem. 9, 660 (2017).
[7] H. Kuramochi et al., Sci. Adv. 5, eaau4490 (2019).

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