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Femtosecond x-ray spectroscopy of an electrocyclic ring-opening reaction

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...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 2017-04, Vol.356 (6333), p.54-59
Main Authors: Attar, Andrew R., Bhattacherjee, Aditi, Pemmaraju, C. D., Schnorr, Kirsten, Closser, Kristina D., Prendergast, David, Leone, Stephen R.
Format: Article
Language:English
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Summary: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-to-valence 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.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.aaj2198