title: An experimental and theoretical study of core-valence double ionisation of acetaldehyde (ethanal).
abstract: Core-valence double ionisation spectra of acetaldehyde (ethanal) are presented at photon energies above the carbon and oxygen 1s ionisation edges, measured by a versatile multi-electron coincidence spectroscopy technique. We use this molecule as a testbed for analyzing core-valence spectra by means of quantum chemical calculations of transition energies. These theoretical approaches range from two simple models, one based on orbital energies corrected by core valence interaction and one based on the equivalent core approximation, to a systematic series of quantum chemical electronic structure methods of increasing sophistication. The two simple models are found to provide a fast orbital interpretation of the spectra, in particular in the low energy parts, while the coverage of the full spectrum is best fulfilled by correlated models. CASPT2 is the most sophisticated model applied, but considering precision as well as computational costs, the single and double excitation configuration interaction model seems to provide the best option to analyze core-valence double hole spectra.
authors.affiliation: Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden and Department of Physics, University of Gothenburg, Origovägen 6B, SE-412 96 Gothenburg, Sweden. raimund.feifel@physics.gu.se.
authors.forename: S
authors.initials: S
authors.lastname: Zagorodskikh
authors.affiliation: Department of Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology, SE-106 91 Stockholm, Sweden and Centre for Molecular Materials Research, University of Oulu, P.O. Box 3000, 90014 Oulu, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Vapa
authors.affiliation: Department of Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology, SE-106 91 Stockholm, Sweden.
authors.forename: O
authors.initials: O
authors.lastname: Vahtras
authors.affiliation: Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden and Department of Physics, University of Gothenburg, Origovägen 6B, SE-412 96 Gothenburg, Sweden. raimund.feifel@physics.gu.se.
authors.forename: V
authors.initials: V
authors.lastname: Zhaunerchyk
authors.affiliation: Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Mucke
authors.affiliation: Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden and Department of Physics, University of Gothenburg, Origovägen 6B, SE-412 96 Gothenburg, Sweden. raimund.feifel@physics.gu.se.
authors.forename: J H D
authors.initials: JH
authors.lastname: Eland
authors.affiliation: Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden and Department of Physics, University of Gothenburg, Origovägen 6B, SE-412 96 Gothenburg, Sweden. raimund.feifel@physics.gu.se.
authors.forename: R J
authors.initials: RJ
authors.lastname: Squibb
authors.affiliation: Department of Physics, Stockholm University, AlbaNova University Center, SE-106 91 Stockholm, Sweden.
authors.forename: P
authors.initials: P
authors.lastname: Linusson
authors.affiliation: Department of Physics, University of Oulu, 90014 Oulu, Finland.
authors.forename: K
authors.initials: K
authors.lastname: Jänkälä
authors.affiliation: Department of Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology, SE-106 91 Stockholm, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Ågren
authors.affiliation: Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden and Department of Physics, University of Gothenburg, Origovägen 6B, SE-412 96 Gothenburg, Sweden. raimund.feifel@physics.gu.se.
authors.forename: R
authors.initials: R
authors.lastname: Feifel