期刊
SCIENCE
卷 356, 期 6333, 页码 54-58出版社
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.aaj2198
关键词
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资金
- U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences [DE-AC02-05CH11231]
- gas phase chemical physics program through the Chemical Sciences Division of Lawrence Berkeley National Laboratory (LBNL)
- Volkswagen Foundation
- NSF Engineering Research Center for Extreme Ultraviolet Science and Technology [EEC-0310717]
- Office of Science, Office of Basic Energy Sciences, of the U.S. DOE [DE-AC02-05CH11231]
- U.S. DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering [DE-AC02-76SF00515]
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 (similar to 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.
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