Anion photoelectron circular dichroism of chiral metal cluster complexes
Final Report Abstract
Chiral molecules ionized by circularly polarized light can show a pronounced forward/backward directional asymmetry in the emission of the electrons, relative to the incident light beam. This effect is known as photoelectron circular dichroism (PECD) and can reach values larger than 10 %, much higher than the conventional dichroism in the absorption of light, thus giving a very sensitive measure of the chiral molecule’s absolute configuration. For the conceptually similar process starting with anions, i.e. photodetachment, such effect was not known at the start of the project. As even the magnitude of a putative anion-PECD wasn’t clear, large parts of the study concentrated on experimental developments focusing on stability and intensity of the sources for chiral anions as well as on the spatial homogeneity in the detection efficiency of electrons in the VMI spectrometer. PECD signals exceeding 1% will be clearly detectable at data accumulation times of few hours. First studies have focused on complexes of the atomic gold anion with chiral molecules like menthone, fenchone, 3-hydroxytetrahydrofuran and alaninol. The choice of these molecules was motivated by results showing a pronounced PECD in their ionization. However, so far no clear PECD signal for the photodetachment of these comparably weakly bound anionic complexes could be detected. A second approach followed the production of cold closed-shell anions by OH-deprotonation. For such anions, preliminary results hint to a possible existence of a PECD effect also in the photodetachment from anions.
