ECAMP 15

Chirality plays a fundamental role in molecular recognition processes. Molecular flexibility is also crucial in molecular recognition, allowing the interacting molecules to adjust their structures and hence optimize the interaction. Methods probing simultaneously chirality and molecular conformation are therefore crucially needed.

This is the case of a recently-introduced chiroptical effect called Photoelectron Circular Dichroism (PECD) 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. PECD happens to be an 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)  asymmetry parameter (for reviews see [1] [2]).
After an introduction to PECD, several results regarding valence-shell PECD on various floppy systems will be presented, belonging to several cases:
• No control on the conformation distribution, so that only a Boltzmann-averaged global PECD response can be measured, as in the case of the amino-acid alanine.[3,4].
• Partial control : case for which owing to a large binding energy difference between two types of conformers, we could observed directly and rationalize with the help of theoretical calculation a conformer-specific PECD as in the case of amino-acid Proline [5], or for which by changing the carrier gas of the molecular beam it was possible to control the conformer distribution [6], as it is the case of 1-Indanol
• Full conformer selection by using a two-photon ns-laser REMPI scheme as we could demonstrate on 1-indanol [7]
Such a sensitivity to conformation is both an asset and a challenge for the ongoing developments of laser-based PECD techniques as a sensitive chiral (bio)chemical analytical tool in the gas phase.

[1] L. Nahon, G. A. Garcia, and I. Powis, J. Elec. Spectro. Relat. Phen. 204, 322 (2015).
[2] R. Hadidi, D. Bozanic, G. Garcia, and L. Nahon, Adv. Physics: X 3, 1477530 (2018).
[3] M. Tia, B. Cunha de Miranda, S. Daly, F. Gaie-Levrel, G. Garcia, I. Powis, and L. Nahon, J. Phys. Chem. Lett. 4, 2698 (2013).
[4] M. Tia, B. Cunha de Miranda, S. Daly, F. Gaie-Levrel, G. A. Garcia, L. Nahon, and I. Powis, J. Phys. Chem. A 118, 2765 (2014).
[5] R. Hadidi, D. K. Božanić, H. Ganjitabar, G. A. Garcia, I. Powis, and L. Nahon, Commun. Chem. 4, 72 (2021).
[6] J. Dupont, V. Lepere, A. Zehnacker, S. Hartweg, G. A. Garcia, and L. Nahon, J. Phys. Chem. Lett. 13, 2313 (2022).
[7] E. Rouquet, J. Dupont, V. Lepere, G. A. Garcia, L. Nahon, and A. Zehnacker, Angew. Chem. Int. Ed. Engl., e202401423 (2024).