Garcia Gustavo A, Dossmann Héloïse, Nahon Laurent, Daly Steven, Powis Ivan
Synchrotron SOLEIL, L'Orme des Merisiers, St. Aubin BP 48, 91192 Gif sur Yvette, France.
Phys Chem Chem Phys. 2014 Aug 14;16(30):16214-24. doi: 10.1039/c4cp01941e.
Photoelectron circular dichroism (PECD), a forward-backward asymmetry along the light propagation direction observed in the angular distribution of photoelectrons formed in the ionization of a chiral gas phase target with circularly polarized light, is becoming an established technique for chiral differentiation. In this work some of the fundamental and analytical properties of PECD are confirmed and explored further through a comparative study of the valence shell photoionization of enantiomerically pure trifluoromethyl-oxirane and methyl-oxirane, namely the sensitivity of PECD to the initial orbital and to chemical substitution. The recorded PECD experimental data and corresponding continuum multiple scattering calculations for the outermost orbitals obtained at various photon energies reveal the dramatic effect of substituting the CF3 and CH3 groups attached at the asymmetric chiral center. The previously unknown trifluoromethyl-oxirane ion spectroscopy and the fragmentation pattern measured by threshold electron/ion coincidence techniques over the first four eVs above the ionization threshold are also presented in this work and assigned through the use of ab initio calculations. The state-selected photochemistry and threshold electron spectroscopy of methyl-oxirane have additionally been recorded to complement previous spectroscopic studies.
光电子圆二色性（PECD）是在用圆偏振光对手性气相靶进行电离时，在光电子角分布中观察到的沿光传播方向的前后不对称性，正成为一种成熟的手性鉴别技术。在这项工作中，通过对映体纯的三氟甲基环氧乙烷和甲基环氧乙烷的价壳层光电离的比较研究，进一步证实和探索了PECD的一些基本和分析特性，即PECD对初始轨道和化学取代的敏感性。在不同光子能量下获得的最外层轨道的记录PECD实验数据和相应的连续多重散射计算揭示了在不对称手性中心连接CF3和CH3基团所产生的显著影响。这项工作还展示了先前未知的三氟甲基环氧乙烷离子光谱以及通过阈值电子/离子符合技术在高于电离阈值的前四个电子伏特范围内测量的碎片模式，并通过使用从头算计算进行了归属。此外，还记录了甲基环氧乙烷的态选择光化学和阈值电子光谱，以补充先前的光谱研究。
