O 1s excitation and ionization processes in the CO₂molecule studied via detection of low-energy fluorescence emission

Abstract

Abstract. Oxygen 1s excitation and ionization processes in the CO 2 molecule have been studied with dispersed and non-dispersed fluorescence spectroscopy as well as with the vacuum ultraviolet (VUV) photon -photoion coincidence technique. The intensity of the neutral O emission line at 845 nm shows particular sensitivity to coreto-Rydberg excitations and core-valence double excitations, while shape resonances are suppressed. In contrast, the partial fluorescence yield in the wavelength window 300-650 nm and the excitation functions of selected O + and C + emission lines in the wavelength range 400-500 nm display all the absorption features. The relative intensity of ionic emission in the visible range increases towards higher photon energies, which is attributed to O 1s shake-off photoionization. VUV photon -photoion coincidence spectra reveal major contributions from the C + and O + ions and a minor contribution from C 2+ . No conclusive changes in the intensity ratios among the different ions are observed above the O 1s threshold. The line shape of the VUV -O + peak carries some information on the initial core excitation.

Production of excited H atoms at the C 1sedge of the methane molecule studied by VUV-photon–photoion and metastable-fragment–photoion coincidence experiments

“…We observed contamination signals in VUV-photonphotoion coincidence spectra during previous measurements [10]. The source of contamination could not be identified at that time, but during the present experiments we realized that those coincidences were caused by electrons that were created when photoions hit the mesh in front of the MCP detector of the ion TOF spectrometer or the MCP itself (see Fig.…”

“…The devices were installed along the electric vector of the linearly polarized incident light. The general setup was already presented in [10], hence only the changes to it are discussed here. First, the gas inlet system via a The front view of the four-sectioned anode is shown on the right side.…”

“…Emission has also been found to persist while crossing the core IP, after which it diminishes gradually as a function of photon energy. That behavior has been attributed to recapture processes following core ionization and Auger decay [10,11]. All in all, low-energy fluorescence emission after core excitation and ionization in small molecules can be explained using the same mechanisms as the production of metastable fragments.…”

“…It is therefore not surprising that fluorescence emission in neutral fragments has been observed at the core edges of many small molecules such as N 2 , H 2 O, NH 3 , CH 4 , and CO 2 [6][7][8][9][10]. Fluorescence emission in fragments is usually enhanced at all core excitations of the studied molecules, but the enhancement has been found to be particularly large, when the initial excitation reaches Rydberg orbitals with n 4 or 5, i.e., in the region close to the core IP [7][8][9][10]. Emission has also been found to persist while crossing the core IP, after which it diminishes gradually as a function of photon energy.…”

Deep core ionic photofragmentation of the CF2Cl2 molecule

“…The Auger transition is occasionally accompanied by the emission of a second electron, i.e., Auger shake-off or successive Auger transitions, making the molecule doubly or triply charged. To help those not familiar with the core excitation, core ionization and Auger decay processes, one refers the reader to a recent paper [27] which presents a compilation of the above mentioned decay processes. Briefly, for species constituted with low-Z atoms, the Auger process prevails predominantly upon the radiative decay.…”