X-ray natural circular dichroism of chiral molecules in liquids
Bonano, Gabriele1,2; Soncini, Cristian1; Jackson, Sebastian Louis1; Ghosh, Jayanta1; Carneiro, Geoffrey3; Menezes Ferreira, Rafael3; Mania, Stefano1; Fondell, Lars4; Eckert, Sebastian4; Nam, Yeonsig5; Asplund, Megan5; Nicolas, Christophe6; Mincigrucci, Riccardo1; Nappini, Silvia7; Magnano, Elena7; De Simone, Monica7; Serrat, Carles8; Masciovecchio, Claudio2; Marroux, Hugo3; Rouxel, Jeremy5; Bozek, John6; Föhlisch, Alexander4; Coreno, Marcello2,9; Chergui, Majed1,10  
1) Elettra-Sincrotrone Trieste, Italy    2) Università di Modena e Reggio Emilia, Italy    3) CEA Paris-Saclay, France    4) BESSY, Helmholtz-Zentrum-Berlin (HZB), Berlin, Germany    5) Advanced Photon Source (APS), Argonne National Laboratory, USA    6) Synchrotron SOLEIL, SACLAY, France           7) IOM-CNR, Italy    8) Universitat Politecnica de Catalunya, Barcelona, Spain    9) ISM-CNR, Italy    10)Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland  
Molecular chirality is central to biology and chemistry. Identification of enantiomers of chiral molecules is based on optical circular dichroism (CD), which was developed starting from the XIXth century on and it measures the absorption difference of left and right circularly polarised light by the sample. CD signals are intrinsically weak, usually 0.1% of the linear absorption, which makes them challenging to measure. Pushing CD spectroscopy into the X-ray domain promises several advantages: a) an enhanced signal (since the terms of light-matter Hamiltonian for CD are inversely proportional to the wavelength), b) element-selectivity, and c) an ability to identify identical but inequivalent atoms in a molecule, not only by their chemical shifts but also their different chiral response, which depends on their position with respect to the chiral centre. Although several theoretical studies have underlined the advantages of soft X-ray natural CD (XNCD), [1–5] its measurement on disordered media (powders) has remained a challenge, and the few studies performed on amino-acid residues and organic molecules do not show clear signatures of chirality, [6–8] probably due to radiation damage, linear dichroism and other effects. 
With the advent of the liquid microjet technique, [9,10] it has become possible to inject liquid samples into vacuum and investigate their soft X-ray absorption both in steady-state and time-resolved studies. We have extended the use of the flat liquid microjets to perform XNCD studies of chiral molecules in solution.

Figure 1: Fenchone O K-edge XNCD spectrum.

We will present for the first-time evidence of XNCD spectra of such systems in the case of fenchone in ethanol. The measurements were carried out at the O K-edge of the molecule, which is not a chiral centre. The results show a good agreement with our theoretical results which are also presented, both in terms of spectral shape as order of magnitude of the intensity.
References

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