Shake-Up and Shake-Off Excitations and Associated Electron Losses in X-Ray Studies of Proteins

Research output: Contribution to journalArticle


Photoionization of an atom by X-rays usually removes an inner shell electron from the atom, leaving behind a perturbed hollow ion whose relaxation may take different routes. In light elements, emission of an Auger electron is common. However, the energy and the total number of electrons released from the atom may be modulated by shake-up and shake-off effects. When the inner shell electron leaves, the outer shell electrons may find themselves in a state that is not an eigen-state of the atom in its surroundings. The resulting collective excitation is called shake-up. If this process also involves the release of low energy electrons from the outer shell, then the process is called shake-off. It is not clear how significant shake-up and shake-off contributions are to the overall ionization of biological materials like proteins. In particular, the interaction between the outgoing electron and the remaining system depends on the chemical environment of the atom, which can be studied by quantum chemical methods. Here we present calculations on model compounds to represent the most common chemical environments in proteins. The results show that the shake-up and shake-off processes affect 20% of all emissions from nitrogen, 30% from carbon, 40% from oxygen, and 23% from sulfur. Triple and higher ionizations are rare for carbon, nitrogen, and oxygen, but are frequent for sulfur. The findings are relevant to the design of biological experiments at emerging X-ray free-electron lasers.


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Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Atom and Molecular Physics and Optics
Original languageEnglish
Pages (from-to)2480-2484
JournalProtein Science
Issue number12
Publication statusPublished - 2001
Publication categoryResearch
Externally publishedYes

Bibliographic note

The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Chemical Physics (S) (011001060)