title: Ultrafast dynamics of acetylacetone (2,4-pentanedione) in the S2 state.
abstract: The dynamics of the enolic form of acetylacetone (E-AcAc) was investigated using a femtosecond pump-probe experiment. The pump at 266 nm excited E-AcAc in the first bright state, S2(pi pi*). The resulting dynamics was probed by multiphoton ionization at 800 nm. It was investigated for 80 ps on the S2(pi pi*) and S1(n pi*) potential energy surfaces. An important step is the transfer from S2 to S1 that occurs with a time constant of 1.4 +/- 0.2 ps. Before, the system had left the excitation region in 70 +/- 10 fs. An intermediate step was identified when E-AcAc traveled on the S2 surface. Likely, it corresponds to an accidental resonance in the detection scheme that is met along this path. More importantly, some clues are given that an intramolecular vibrational energy relaxation is observed, which transfers excess vibrational energy from the enolic group O-H to the other modes of the molecule. The present multistep evolution of excited E-AcAc probably also describes, at least qualitatively, the dynamics of other electronically excited beta-diketones.
authors.affiliation: Laboratoire Francis Perrin (CNRS-URA-2453), DSM/IRAMIS/Service des Photons, Atomes et Molécules, C.E.A. Saclay, F-91191 Gif-sur-Yvette cedex, France.
authors.forename: Lionel
authors.initials: L
authors.lastname: Poisson
authors.forename: Pascale
authors.initials: P
authors.lastname: Roubin
authors.forename: Stéphane
authors.initials: S
authors.lastname: Coussan
authors.forename: Benoît
authors.initials: B
authors.lastname: Soep
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Mestdagh
mesh_terms: D006860:Hydrogen Bonding; D015394:Molecular Structure; D010422:Pentanones / Q000737:chemistry*; D011789:Quantum Theory; D013997:Time Factors
chemical_list: D010422:Pentanones; C008790:acetylacetone