Femtosecond x-ray spectroscopy of an electrocyclic ring-opening reaction
- Author(s): Attar, AR
- Bhattacherjee, A
- Pemmaraju, CD
- Schnorr, K
- Closser, KD
- Prendergast, D
- Leone, SR
- et al.
Published Web Locationhttps://doi.org/10.1126/science.aaj2198
© 2016 by the American Association for the Advancement of Science; all rights reserved. The ultrafast light-activated electrocyclic ring-opening reaction of 1,3-cyclohexadiene is a fundamental prototype of photochemical pericyclic reactions. Generally, these reactions are thought to proceed through an intermediate excited-state minimum (the so-called pericyclic minimum), which leads to isomerization via nonadiabatic relaxation to the ground state of the photoproduct. Here, we used femtosecond (fs) soft x-ray spectroscopy near the carbon K-edge (∼284 electron volts) on a table-top apparatus to directly reveal the valence electronic structure of this transient intermediate state. The core-tovalence spectroscopic signature of the pericyclic minimum observed in the experiment was characterized, in combination with time-dependent density functional theory calculations, to reveal overlap and mixing of the frontier valence orbital energy levels. We show that this transient valence electronic structure arises within 60 ± 20 fs after ultraviolet photoexcitation and decays with a time constant of 110 ± 60 fs.
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