TY  - JOUR
A1  - Wolf, Thomas
A1  - Gühr, Markus
T1  - Photochemical pathways in nucleobases measured with an X-ray FEL
JF  - Philosophical Transactions of the Royal Society of London, Series A : Mathematical, Physical and Engineering Sciences
N2  - The conversion of light energy into other molecular energetic degrees of freedom is often dominated by ultrafast, non-adiabatic processes. Femtosecond spectroscopy with optical pulses has helped in shaping our understanding of crucial processes in molecular energy-conversion. The advent of new, ultrashort and bright X-ray free electron laser sources opens the possibility to use X-ray-typical element and site sensitivity for ultrafast molecular research. We present two types of spectroscopy, ultrafast Auger and ultrafast X-ray absorption spectroscopy, and discuss their sensitivity to molecular processes. While Auger spectroscopy is able to monitor bond distance changes in the vicinity of an X-ray created core hole, near-edge absorption spectroscopy can deliver high-fidelity information on non-adiabatic transitions involving lone-pair orbitals. We demonstrate these features on the example of the UV-excited nucleobase thymine, investigated at the oxygen K-edge. We find a C-O bond elongation in the Auger data in addition to pi pi*/n pi* non-adiabatic transition in X-ray near-edge absorption. We compare the results from both methods and draw a conclusive scenario of non-adiabatic molecular relaxation after UV excitation.
KW  - nucleobase
KW  - time-resolved X-ray probing
KW  - Auger decay
KW  - femtosecond laser spectroscopy
Y1  - 2019
U6  - https://doi.org/10.1098/rsta.2017.0473
SN  - 1364-503X
SN  - 1471-2962
VL  - 377
IS  - 2145
PB  - Royal Society
CY  - London
ER  -