title: Femtosecond x-ray spectroscopy of an electrocyclic ring-opening reaction.
abstract: 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 tabletop 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.
authors.affiliation: Department of Chemistry, University of California, Berkeley, CA 94720, USA.|Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Andrew R
authors.identifier: 0000-0002-9509-3857
authors.initials: AR
authors.lastname: Attar
authors.affiliation: Department of Chemistry, University of California, Berkeley, CA 94720, USA.|Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Aditi
authors.identifier: 0000-0001-7146-1128
authors.initials: A
authors.lastname: Bhattacherjee
authors.affiliation: The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.|Theory Institute for Materials and Energy Spectroscopies, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
authors.forename: C D
authors.identifier: 0000-0002-9016-7044
authors.initials: CD
authors.lastname: Pemmaraju
authors.affiliation: Department of Chemistry, University of California, Berkeley, CA 94720, USA.|Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Kirsten
authors.identifier: 0000-0002-5519-440X
authors.initials: K
authors.lastname: Schnorr
authors.affiliation: The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Kristina D
authors.initials: KD
authors.lastname: Closser
authors.affiliation: The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: David
authors.identifier: 0000-0003-0598-1453
authors.initials: D
authors.lastname: Prendergast
authors.affiliation: Department of Chemistry, University of California, Berkeley, CA 94720, USA. srl@berkeley.edu.|Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.|Department of Physics, University of California, Berkeley, CA 94720, USA.
authors.forename: Stephen R
authors.identifier: 0000-0003-1819-1338
authors.initials: SR
authors.lastname: Leone