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Title: Probing the molecular basis of photochemistry and photophysics with vibrational coherence spectroscopy
Author: Schnedermann, Christoph
ISNI:       0000 0004 6063 3205
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2015
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We present a time-domain impulsive vibrational spectroscopy (IVS) setup capable of recording background- and baseline-free Raman spectra of excited electronic states in condensed-phase molecular systems. The setup records vibrational Raman spectra from 50-3000 cm-1 and is readily extended to follow spectral evolutions with a time resolution of < 20 fs, opening up the possibility for multi-dimensional Raman spectroscopy. Based on the setup, we explore a wide range of photochemical reactions aimed at gaining fundamental insights in the chemistry of excited electronic states. In rhodopsin, we investigate the consequences of vibrational wavepacket motion through a conical intersection. We identify the C11-H hydrogen out-of-plane mode as a coupling mode and devise a general model of how vibrational coherences can be used to obtain otherwise inaccessible structural information. In a second experiment, we determine the photoproduct distribution and dynamics upon isotopic substitution of selected hydrogen atoms along the retinal backbone. The results suggest a re-definition of the traditional Jablonski diagram for ultrafast photoreactions, which proceed faster than vibrational relaxation. In channelrhodopsin-1, we structurally characterise the primary photoproduct in the photocycle to be of 13-cis character. The study highlights the capabilities of IVS to obtain structural information for short-lived intermediate structures which are otherwise challenging to obtain. For the green fluorescent protein and all-trans retinal protonated Schiff base, we identify key excited-state (intermediate) structures and complement the studies with multi-dimensional Raman spectroscopy. The results provide a first picture of the structural origin of energy flow directly after photoexcitation. This thesis emphasises the capabilities of IVS beyond a proof-of-principle experiment and outlines the high potential of time-domain vibrational spectroscopy to reveal detailed structural information on ultrafast processes with high temporal resolution and sensitivity.
Supervisor: Kukura, Philipp Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available