近日，以色列理工学院Neufeld, Ofer团队研究了光电子手性二色性的对称性和选择规则
光电子圆二色性（PECD）是一种通过圆偏振光照射随机取向的手性分子、使其发生光电离，并对光电子进行动量分辨测量的方法。该方案允许在电偶极近似下实现手性光-物质相互作用（避免使用较弱的磁偶极相互作用），从而以光发射前后不对称性的形式产生巨大的手性信号。近年来，研究者开始探索更复杂的PECD实现方案，例如用经偏振精密调控的光场（如双色、非共线等）替代圆偏振光；其中一些方案甚至无需圆偏振分量，仍能产生显著的手性信号。然而，广义的激光场对称性与不对称性同PECD选择定则之间的关联尚未得到系统阐释。
研究组基于群论解析推导了这种关联，并针对具有动态反演对称性及非真旋转对称性的光场，预测了两种先前未知的PECD选择定则。他们还提出利用双色双椭圆场来打破典型光谱中的对称性，从而有望为超快分辨测量提供更丰富的信息。通过在手性分子原型溴氯氟甲烷中进行最先进的从头算数值模拟，研究组验证了所有理论结果，并为实验提供了预测。该工作为分析定制光场下的PECD提供了系统性研究路径，解决了该领域长期存在的问题，有望推动新型PECD实验与理论研究的发展。
附：英文原文
Title: Symmetries and selection rules in photoelectron chiral dichroism
Author: Neufeld, Ofer
Issue&Volume: 2025-12-22
Abstract: Photoelectron circular dichroism (PECD) is a method whereby randomly oriented chiral molecules are irradiated by circularly polarized light (CPL), photoionizing electrons, which are measured in a momentum-resolved manner. This scheme permits chiral light–matter interactions within the electric-dipole approximation (avoiding weak magnetic-dipole interactions), yielding huge chiral signals in the form of a forward–backward asymmetry in photoemission. Recently, more intricate realizations of PECD have been explored where the CPL is replaced with elaborate polarization-tailored light (e.g., bichromatic, noncollinear, etc.), some of which do not even require circularly polarized components, but still lead to massive chiral signals. However, the connection between generalized symmetries and asymmetries of the laser drive and selection rules in PECD have not yet been derived. Here, we formulate this connection analytically from group theory, also predicting two previously unknown selection rules for PECD from fields with dynamical inversion and improper-rotational symmetries. We further propose bichromatic bielliptical fields for breaking symmetries in typical spectra, yielding potentially more information for ultrafast-resolved measurements. We numerically demonstrate all of our results with state-of-the-art ab-initio simulations in the archetypal chiral molecule, Bromochlorofluoromethane, providing predictions for experiments. Our work presents a roadmap for analyzing PECD from tailored light and resolves a long-standing issue in the field. It should motivate theoretical and experimental investigations in novel PECD set-ups.
DOI: 10.1073/pnas.2504816122
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2504816122