  Chirality is a structural property of molecules lacking mirror symmetry that
has strong implications in diverse fields, ranging from life to materials
sciences. Established spectroscopic methods that are sensitive to chirality,
such as circular dichroism (CD), exhibit weak signal contributions on an
achiral background. Helical dichroism (HD), which is based on the orbital
angular momentum (OAM) of light, offers a new approach to probe molecular
chirality, but it has never been demonstrated on disordered samples.
Furthermore, in the optical domain the challenge lies in the need to transfer
the OAM of the photon to an electron that is localized on an {\AA}-size
orbital. Here, we overcome this challenge using hard X-rays with spiral Fresnel
zone, which can induce an OAM. We present the first HD spectra of a disordered
powder sample of enantiopure molecular complexes of [Fe(4,4'-diMebpy)3]2+ at
the iron K-edge (7.1 keV) with OAM-carrying beams. The HD spectra exhibit the
expected inversions of signs switching from a left to a right helical wave
front or from an enantiomer to the other. The asymmetry ratios for the HD
spectra are within one to five percent for OAM beams with topological charges
of one and three. These results open a new window into the studies of molecular
chirality and its interaction with the orbital angular momentum of light.

Chemical Physics;Optics