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Title:Ultrafast molecular three-electron collective auger decay
Author(s):Feifel, Raimund
Abstract:A new class of many-electron Auger transitions in atoms was initially proposed over 40 years ago, but the first tentative evidence for its real existence was only adduced by Lee et al. 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
Rights Information:Copyright 2016 by the authors
Date Available in IDEALS:2016-08-22

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