title: Field ionization of high-Rydberg fragments produced after inner-shell photoexcitation and photoionization of the methane molecule.
abstract: We have studied the production of neutral high-Rydberg (HR) fragments from the CH4 molecule at the C 1s → 3p excitation and at the C 1s ionization threshold. Neutral fragments in HR states were ionized using a pulsed electric field and the resulting ions were mass-analyzed using an ion time-of-flight spectrometer. The atomic fragments C(HR) and H(HR) dominated the spectra, but molecular fragments CH(x)(HR), x = 1-3, and H2(HR) were also observed. The production of HR fragments is attributed to dissociation of CH4(+) and CH4(2+) ions in HR states. Just above the C 1s ionization threshold, such molecular ionic states are created when the C 1s photoelectron is recaptured after single or double Auger decay. Similar HR states may be reached directly following resonant Auger decay at the C 1s → 3p resonance. The energies and geometries of the parent and fragment ions have been calculated in order to gain insight into relevant dissociation pathways.
authors.affiliation: Consiglio Nazionale delle Ricerche-Istituto Officina dei Materiali, Laboratorio TASC, 34149 Trieste, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Kivimäki
authors.affiliation: Department of Physics, Lund University, P.O. Box 118, 22100 Lund, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Sankari
authors.affiliation: Department of Physics, University of Oulu, P.O. Box 3000, 90014 Oulu, Finland.
authors.forename: J A
authors.initials: JA
authors.lastname: Kettunen
authors.affiliation: MAX IV Laboratory, Lund University, P.O. Box 118, 22100 Lund, Sweden.
authors.forename: C
authors.initials: C
authors.lastname: Stråhlman
authors.affiliation: Colegio Los Naranjos, Fuenlabrada, 28941 Madrid, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Álvarez Ruiz
authors.affiliation: Elettra-Sincrotrone Trieste, Area Science Park Basovizza, 34149 Trieste, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Richter