title: Valence shell electronic spectroscopy of isoprene studied by theoretical calculations and by electron scattering, photoelectron, and absolute photoabsorption measurements.
abstract: The first ab initio calculations (vertical energies and oscillator strengths) are reported for the neutral electronic transitions of isoprene (2-methyl-1,3-butadiene), CH(2)CHC(CH(3))CH(2). The VUV photoabsorption spectroscopy of the molecule is presented in the energy range 4.6 to 10.8 eV (270-125 nm) with the highest resolution yet reported above 6.05 eV, revealing new spectral features. Valence and Rydberg transitions have been assigned in accordance with the theoretical results and the associated vibronic series have been analysed. The absolute photoabsorption cross sections at energies below 6.89 eV have been used to calculate the photolysis lifetime of isoprene in the upper stratosphere (20-50 km). Electron energy loss spectroscopy (EELS) measurements have enabled further photoabsorption cross sections to be derived in the range 9-28 eV. The first ab initio calculations have been carried out to determine excitation energies to the lowest energy ionic states of isoprene. The calculations are compared with the He(i) photoelectron spectrum (8 to 17 eV) and new vibrational structure is observed in the first photoelectron band.
authors.affiliation: Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors.forename: G
authors.initials: G
authors.lastname: Martins
authors.forename: A M
authors.initials: AM
authors.lastname: Ferreira-Rodrigues
authors.forename: F N
authors.initials: FN
authors.lastname: Rodrigues
authors.forename: G G B
authors.initials: GG
authors.lastname: de Souza
authors.forename: N J
authors.initials: NJ
authors.lastname: Mason
authors.forename: S
authors.initials: S
authors.lastname: Eden
authors.forename: D
authors.initials: D
authors.lastname: Duflot
authors.forename: J-P
authors.initials: JP
authors.lastname: Flament
authors.forename: S V
authors.initials: SV
authors.lastname: Hoffmann
authors.forename: J
authors.initials: J
authors.lastname: Delwiche
authors.forename: M-J
authors.initials: MJ
authors.lastname: Hubin-Franskin
authors.forename: P
authors.initials: P
authors.lastname: Limão-Vieira
mesh_terms: D002070:Butadienes / Q000737:chemistry*; D045782:Hemiterpenes / Q000737:chemistry*; D010420:Pentanes / Q000737:chemistry*; D010782:Photolysis; D011789:Quantum Theory; D046590:Spectroscopy, Electron Energy-Loss; D013816:Thermodynamics
chemical_list: D002070:Butadienes; D045782:Hemiterpenes; D010420:Pentanes; C005059:isoprene