title: Threshold energies for single-carbon knockout from polycyclic aromatic hydrocarbons.
abstract: We have measured absolute cross sections for ultrafast (femtosecond) single-carbon knockout from polycyclic aromatic hydrocarbon (PAH) cations as functions of He–PAH center-of-mass collision energy in the 10–200 eV range. Classical molecular dynamics (MD) simulations cover this range and extend up to 105 eV. The shapes of the knockout cross sections are well-described by a simple analytical expression yielding experimental and MD threshold energies of EthExp = 32.5 ± 0.4 eV and EthMD = 41.0 ± 0.3 eV, respectively. These are the first measurements of knockout threshold energies for molecules isolated in vacuo. We further deduce semiempirical (SE) and MD displacement energies, i.e., the energy transfers to the PAH molecules at the threshold energies for knockout, of TdispSE = 23.3 ± 0.3 eV and TdispMD = 27.0 ± 0.3 eV. The semiempirical results compare favorably with measured displacement energies for graphene (Tdisp = 23.6 eV).
authors.affiliation: Department of Physics, Stockholm University , Stockholm SE-106 91, Sweden.|Department of Physics and Astronomy, Aarhus University , DK-8000 Aarhus C, Denmark.
authors.forename: M H
authors.initials: MH
authors.lastname: Stockett
authors.affiliation: Department of Physics, Stockholm University , Stockholm SE-106 91, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Gatchell
authors.affiliation: Department of Physics, Stockholm University , Stockholm SE-106 91, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Chen
authors.affiliation: Department of Physics, Stockholm University , Stockholm SE-106 91, Sweden.
authors.forename: N
authors.initials: N
authors.lastname: de Ruette
authors.affiliation: Department of Physics, Stockholm University , Stockholm SE-106 91, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Giacomozzi
authors.affiliation: Department of Physics, Stockholm University , Stockholm SE-106 91, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Wolf
authors.affiliation: Department of Physics, Stockholm University , Stockholm SE-106 91, Sweden.
authors.forename: H T
authors.initials: HT
authors.lastname: Schmidt
authors.affiliation: Department of Physics, Stockholm University , Stockholm SE-106 91, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Zettergren
authors.affiliation: Department of Physics, Stockholm University , Stockholm SE-106 91, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Cederquist
keywords: cross section; molecular dynamics; polycyclic aromatic hydrocarbons; single-carbon knockout; threshold energy