What is it about?

This is a theoretical paper aimed at exploring the information content of both linear and (in particular) nonlinear spectroscopy in the X-ray window. In nonlinear spectroscopy a sample (e.g. of molecules) is interrogated by multiple laser pulses to get insight into its properties. Nonlinear spectroscopy with X-ray pulses is becoming a reality in fast developing X-ray Free electron laser facilities (e.g. LCLS in the USA, Fermi in Italy, the European XFEL in Germany). Still it is not known a-priori what could be the insight one can get from these experiments. Here, by combining very accurate calculations of the microscopic (quantum-mechanical) properties of a given molecule (the so called ESCA molecole, or ethyl trifluoroacetate) to the simulation of spectroscopy, we demonstrated that one could in principle infer the positioning of the atoms in the molecule unraveling the network of their interaction.

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Why is it important?

On the one hand, the relevance of this work is linked in general to the broad topic of spectroscopy, i.e. using light to interrogate molecular systems and understand their properties. This is important from the purely desire of understanding the physical world, and also to discover molecules for specific applications (in electronics, medicine, energy). On the other hand, this is one of the few works that show how X-ray pulses, at the XFEL facilities, are unique for their ability to probe specific properties to which other spectroscopic techniques (that e.g. employ visible or UV light) are blind to.

Perspectives

This contribution opens up a series of possible nonlinear spectroscopy experiments that we hope will soon become doable also in experimental facilities.

Francesco Segatta
Universita degli Studi di Bologna

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This page is a summary of: X-ray linear and non-linear spectroscopy of the ESCA molecule, The Journal of Chemical Physics, September 2019, American Institute of Physics, DOI: 10.1063/1.5116699.
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