Chirality is a structural property of molecules lacking mirror symmetry that has strong implications in diverse fields, ranging from life sciences to materials science. Chirality-sensitive spectroscopic methods, such as circular dichroism, exhibit weak signal contributions on an achiral background. Helical dichroism, 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 ångström-size orbital. Here we overcome this challenge using hard X-rays with spiral Fresnel zone plates, which can induce an OAM. We present the helical dichroism spectra of a disordered powder sample of enantiopure salts of the molecular complex of [Fe(4,4′-diMebpy)₃]²⁺ at the iron K edge (7.1 keV) with OAM-carrying beams. The asymmetry ratios for the helical dichroism 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 OAM of light.

手性是缺乏镜像对称性的分子的一种结构特性，在从生命科学到材料科学的各个领域都具有重要意义。手性敏感的光谱方法，例如圆二色性，在非手性背景上表现出微弱的信号贡献。基于光的轨道角动量 (OAM) 的螺旋二色性为探测分子手性提供了一种新方法，但它从未在无序样品上得到证实。此外，在光学领域，挑战在于需要将光子的 OAM 转移到位于 Ångström 大小轨道上的电子。在这里，我们使用带有螺旋菲涅耳波带板的硬 X 射线克服了这一挑战，它可以诱导 OAM。₃ ] ²⁺在铁 K 边缘 (7.1 keV) 与 OAM 承载梁。对于拓扑电荷为 1 和 3 的 OAM 光束，螺旋二色光谱的不对称比在 1% 到 5% 以内。这些结果为分子手性及其与光的 OAM 相互作用的研究打开了一个新窗口。