MBI Colloquium

Mittwoch, 05. März 2025 // 14.00 -

Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie

Max-Born-Straße 2a, 12489 Berlin
Max Born Hall

Recent results on Photoelectron Circular Dichroism (PECD): from static measurements to time-resolved site-specific explorations

Prof. Laurent Nahon | Synchrotron SOLEIL, Saint Aubin, France

Chirality is ubiquitous in nature, especially in the biosphere, and the so-called chiral recognition process is fundamental for metabolism and drug action. Within a bottom/up approach of molecular complexity, the study of isolated, substrate- and solvent-free chiral species is crucial, but classical chiroptical probes such as Circular Dichroism (CD) in absorption are poorly-adapted to dilute matter because of their very weak associated asymmetries.

At the opposite, two decades ago was introduced a new chiroptical effect called Photoelectron Circular Dichroism (PECD), allowed in the electric dipole approximation, leading to very intense (up to 40 %) forward/backward asymmetries, with respect to the photon axis, in the angular distribution of photoelectrons produced by circularly-polarized light ionization of gas phase pure enantiomers (see [1]). PECD happens to be a universal, orbital-specific, photon energy dependent chiroptical effect and is a subtle probe of the molecular potential being very sensitive to static molecular structures such as conformers, isomers, clusters, as well as to vibrational motion, much more so than other observables in photoionization such as the cross section (Photoelectron Spectrum-PES) or the usual (achiral) β asymmetry parameter (for a review see [2]). Therefore, PECD studies have both a fundamental and an analytical interest.

Several recent results regarding static one VUV-photon valence-shell PECD will be presented, including the specific sensitivity of PECD to conformations [3], completed by a recent two-photon REMPI demonstration of conformer-selective PECD [4], as well as a first evidence of induced-PECD onto an achiral chromophore within a molecular complex [5].

We will then move towards Time-Resolved PECD (TR-PECD), performed with the FERMI FEL enabling the chemical-specific, site-specific, and enantio-sensitive observation of the electronic structure changes of a transiently photoexcited chiral molecule via core-shell TR-PECD [6].

[1] I. Powis, Photoelectron Circular Dichroism in Chiral Molecules, Adv. Chem. Phys. 138, 267 (2008).

[2] R. Hadidi, D. Bozanic, G. Garcia, L. Nahon, Electron asymmetries in the photoionization of chiral molecules: possible astrophysical implications, Adv. Phys. X 3, 1477530 (2018).

[3] J. Dupont, V. Lepere, A. Zehnacker, S. Hartweg, G.A. Garcia, L. Nahon, Photoelectron Circular Dichroism as a Signature of Subtle Conformational Changes: The Case of Ring Inversion in 1-Indanol, J. Phys. Chem. Lett. 13, 2313 (2022).

[4] E. Rouquet, J. Dupont, V. Lepere, G.A. Garcia, L. Nahon, A. Zehnacker, Conformer-Selective Photoelectron Circular Dichroism, Angew. Chem. Int. Ed. Engl., e202401423 (2024).

[5] E. Rouquet, M. Roy Chowdhury, G.A. Garcia, L. Nahon, J. Dupont, V. Lepère, K. Le Barbu-Debus, A. Zehnacker, Induced photoelectron circular dichroism onto an achiral chromophore, Nat. Commun. 14, 6290 (2023).

[6] D. Faccialà et al., Time-Resolved Chiral X-Ray Photoelectron Spectroscopy with Transiently Enhanced Atomic Site Selectivity: A Free-Electron Laser Investigation of Electronically Excited Fenchone Enantiomers, Phys. Rev. X 13, 011044 (2023).