Geng, T;
Ehrmaier, J;
Schalk, O;
Richings, GW;
Hansson, T;
Worth, G;
Thomas, RD;
(2020)
Time-Resolved Photoelectron Spectroscopy Studies of Isoxazole and Oxazole.
Journal of Physical Chemistry A
, 124
(20)
pp. 3984-3992.
10.1021/acs.jpca.9b11788.
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Abstract
The excited state relaxation pathways of isoxazole and oxazole upon excitation with UV-light were investigated by nonadiabatic ab initio dynamics simulations and time-resolved photoelectron spectroscopy. Excitation of the bright ππ*-state of isoxazole predominantly leads to ring-opening dynamics. Both the initially excited ππ*-state and the dissociative πσ*-state offer a combined barrier-free reaction pathway, such that ring-opening, defined as a distance of more than 2 Å between two neighboring atoms, occurs within 45 fs. For oxazole, in contrast, the excited state dynamics is about twice as slow (85 fs) and the quantum yield for ring-opening is lower. This is caused by a small barrier between the ππ*-state and the πσ*-state along the reaction path, which suppresses direct ring-opening. Theoretical findings are consistent with the measured time-resolved photoelectron spectra, confirming the timescales and the quantum yields for the ring-opening channel. The results indicate that a combination of time-resolved photoelectron spectroscopy and excited state dynamics simulations can explain the dominant reaction pathways for this class of molecules. As a general rule, we suggest that the antibonding σ*-orbital located between the oxygen atom and a neighboring atom of a five-membered heterocyclic system provides a driving force for ring-opening reactions, which is modified by the presence and position of additional nitrogen atoms.
Type: | Article |
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Title: | Time-Resolved Photoelectron Spectroscopy Studies of Isoxazole and Oxazole. |
Location: | United States |
Open access status: | An open access version is available from UCL Discovery |
DOI: | 10.1021/acs.jpca.9b11788 |
Publisher version: | https://doi.org/10.1021/acs.jpca.9b11788 |
Language: | English |
Additional information: | This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. |
UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry |
URI: | https://discovery.ucl.ac.uk/id/eprint/10100390 |
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