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 Title: Ultrafast molecular three-electron collective auger decay Author(s): Feifel, Raimund Subject(s): Synchrotron Abstract: A new class of many-electron Auger transitions in atoms was initially proposed over 40 years ago\footnote{G.N. Ogurtsov et al., Sov. Phys. Tech. Phys. 15, 1656 (1971) and V.V. Afrosimov et al., JETP Lett. 21, 249 (1975).}, but the first tentative evidence for its real existence was only adduced by Lee et al.\footnote{I. Lee, R. Wehlitz, U. Becker and M. Ya. Amusia, J. Phys. B: At. Mol. Opt. Phys. 26, L41 (1993).} in 1993, on the basis of the resonant Auger spectrum of Kr. Using a multi-electron coincidence technique with synchrotron radiation, we unambiguously showed very recently that the transition suggested by Lee et al. in Kr really does take place, but with a rather small branching ratio\footnote{J.H.D. Eland, R.J. Squibb, M. Mucke, S. Zagorodskikh, P. Linusson, and R. Feifel, New J. Phys. 17, 122001 (2015).}. Related inter-atomic three-electron transitions in rare gas clusters were recently predicted by Averbukh and Kolorenč\footnote{V. Averbukh and P. Kolorenč, Phys. Rev. Lett. 103, 183001 (2009).} and demonstrated by Ouchi et al.\footnote{T. Ouchi et al., Phys. Rev. Lett. 107, 053401 (2011).}. From consideration of the energy levels involved it seems that the basic three-electron process could occur in molecules too, wherever a double inner-valence shell vacancy lies at a higher energy than the molecular triple ionisation onset. Experiments on CH$_3$F reveal for the first time the existence of this new decay pathway there\footnote{R. Feifel et al., Phys. Rev. Lett. 116, 073001 (2016).}, and calculations show that despite its three-electron nature, its effective oscillator strength is orders of magnitudes higher than in atoms, allowing an efficient competition with both molecular dissociation and two-electron decay channels on the ultrafast time scale. The dramatic enhancement of the molecular three-electron Auger transition can be explained in terms of a partial breakdown of the molecular orbital picture of ionisation. We predict that the collective decay pathway will be significant in a wide variety of heteroatomic molecules ionised by extreme UV and soft X-rays, particularly at Free-Electron-Lasers where double inner-shell vacancies can be created efficiently by two-photon transitions. Issue Date: 2016-06-24 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper/Presentation Type: Text Language: En URI: http://hdl.handle.net/2142/91311 Rights Information: Copyright 2016 by the authors Date Available in IDEALS: 2017-01-26
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