The electron-energy-loss spectra of methane tagged with Lyman-α photons in the range of doubly excited states

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The cross sections for the generation of a pair of fluorescence photons in the photoexcitation of O 2 differential with respect to solid angles for the emission of the photon pair have been measured as a function of incident photon energy in the range 23-47 eV using the photon-photon coincidence method, the (γ , 2γ ) method, to investigate the inner-valence excited states and multiply excited states of O 2 as superexcited states. Four superexcited states of O 2 with the 3 − u or 3 u symmetry have been newly found around 29, 36, 38 and 44 eV in the measured cross section curve free from ionization. It turns out that they are inner-valence excited states and multiply excited states. Two remarkable points are shown: (1) there exist superexcited states of O 2 dissociating into neutral fragments even in the energy range above the double-ionization potential of O 2 at 36.13 eV and (2) the values of the doubly differential cross sections decrease to a large extent around the double-ionization potential with increasing incident photon energy, both of which have been compared with the results of N 2 by our previous (γ , 2γ ) experiment. The origin of (2) is discussed in detail.

Section: Introductionmentioning

confidence: 99%

Inner-valence excited and multiply excited states of molecular oxygen around the double-ionization potential as probed by a pair of fluorescence photons

Odagiri

Miyagi

Murata

et al. 2009

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“…These authors found much larger cross sections due to doubly excited states than those expected within the independent electron model. Optically forbidden doubly excited states of CH 4 , NH 3 and H 2 O were investigated by measuring the electron energy loss spectra tagged with the Lyman-α fluorescence [11,[13][14][15]. However, in the energy range higher than the threshold for the production of excited states of the molecular ion, the dissociative ionizations accompanied by fluorescence emissions are possible and the cross section curves are dominated by such dissociative direct ionizations, preventing us from observing higher-lying multiply excited states.…”

Section: Abmentioning

confidence: 99%

Three-body neutral dissociations of a multiply excited water molecule around the double ionization potential

Odagiri

Nakano

Tanabe

et al. 2012

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The cross sections for emission of two fluorescence photons from a pair of excited fragments in photoexcitation of H2O have been measured as a function of the incident photon energy using the photon–photon coincidence technique. The cross section increased in the range 30–45 eV, i.e. in the vicinity of the double ionization potential of H2O. The increase of the cross section was attributed to three-body neutral dissociations of a water molecule via multiply excited states: H2O** → H(2p) + OH** → H(2p) + H(2p) + O(3P). Some multiply excited states of H2O were also found in the cross section curve around 65 eV.

“…Because the large contribution of ionization is eliminated from an electron energy-loss spectrum, buried doubly excited peaks appear in the spectrum. Odagiri et al studied the doubly excited states of simple molecules, such as H 2 , D 2 , N 2 , CH 4 and NH 3 using Co-EELS [20][21][22][23][24][25][26][27], measurements of fluorescence cross section and (γ , 2γ ) spectroscopy [28][29][30]. In particular, they greatly contributed to the elucidation of the doubly excited states of molecular hydrogen and found optically forbidden doubly excited states.…”

Section: Introductionmentioning

confidence: 99%

Doubly excited states of ammonia by scattered electron–ion coincidence measurements

Yamamoto¹,

Sakai²

2012

To obtain information on the optically forbidden doubly excited states of ammonia (NH3), we performed scattered electron–ion coincidence measurements. First, we observed scattered electrons using electron energy-loss spectroscopy and determined the generalized oscillator strength distribution (GOSD) under 200 eV incident electron energy at a scattering angle of 8°. Ionic GOSDs were also determined by combination with the coincidence signal, which was observed by the time-of-flight mass spectrometer at each energy-loss value, for each ion. The total and partial ionic GOSDs were compared with the experimental results of both photon and fast electron impact. Moreover, the neutral GOSD determined by subtracting the total ionic GOSD from the total was compared with previous results. In addition to the optically forbidden doubly excited states, which were identified by Kato et al (2003 J. Phys. B: At. Mol. Opt. Phys. 36 3541) and Ishikawa et al (2008 J. Phys. B: At. Mol. Opt. Phys. 41 195204), we found a new optically forbidden doubly excited state at around 35 eV.