Re: [Ifeffit] lifetime broadening of pre-edge peaks
Hi Matthew, The lifetime broadening of the XANES features is determined by the time of life of the final excited state. This two-particle excitation includes the core hole and the photoelectron. The core hole may decay due to the various radiation or non radiation processes. The photoelectron state may decay due to inelastic collisions, plasmon excitations, etc. The time of life of the core hole, I believe, does not depend on the photon energy whilst the last is near the absorption edge. But it is not true for the photoelectron. It is better to write “photoelectron” because some of the pre-edge peaks which exist in the transition metal oxides spectra are in fact X-ray excitons and no photoemission can be observed. In these cases the final states are bound states and it is purely many electron effect caused by the core-hole - “photoelectron” interaction. For those pre-edge peaks the life time broadening is determined entirely by the core-hole life time. But as soon as photoelectron jumps to the conduction band the mechanisms of its inelastic scattering turn on and one should take into account the time of life of photoelectron (now without quotes). Unfortunately, it is difficult to determine which pre-edge peaks are excitonic and which are not. As it was already mentioned there are other mechanisms of broadening of the pre-edge peaks. For diamagnetic atoms it is thermal vibrations, for paramagnetic ones it is multiplet interactions as well. Good luck. Victor Krayzman.
How significant are the photoelectron effects in hard X-rays compared with the core-hole effect? What I'm really after is a criterion for determining, at least roughly, how narrow a real, physical feature can be. mam ----- Original Message ----- From: vikrai@comcast.net To: ifeffit@millenia.cars.aps.anl.gov Sent: Monday, October 10, 2011 6:37 PM Subject: Re: [Ifeffit] lifetime broadening of pre-edge peaks Hi Matthew, The lifetime broadening of the XANES features is determined by the time of life of the final excited state. This two-particle excitation includes the core hole and the photoelectron. The core hole may decay due to the various radiation or non radiation processes. The photoelectron state may decay due to inelastic collisions, plasmon excitations, etc. The time of life of the core hole, I believe, does not depend on the photon energy whilst the last is near the absorption edge. But it is not true for the photoelectron. It is better to write “photoelectron” because some of the pre-edge peaks which exist in the transition metal oxides spectra are in fact X-ray excitons and no photoemission can be observed. In these cases the final states are bound states and it is purely many electron effect caused by the core-hole - “photoelectron” interaction. For those pre-edge peaks the life time broadening is determined entirely by the core-hole life time. But as soon as photoelectron jumps to the conduction band the mechanisms of its inelastic scattering turn on and one should take into account the time of life of photoelectron (now without quotes). Unfortunately, it is difficult to determine which pre-edge peaks are excitonic and which are not. As it was already mentioned there are other mechanisms of broadening of the pre-edge peaks. For diamagnetic atoms it is thermal vibrations, for paramagnetic ones it is multiplet interactions as well. Good luck. Victor Krayzman. ------------------------------------------------------------------------------ _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
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