Femtosecond photoelectron circular dichroism of chemical reactions

Abstract

Understanding the chirality of molecular reaction pathways is essential for a broad range of fundamental and applied sciences. However, the current ability to probe chirality on the time scale of primary processes underlying chemical reactions remains very limited. Here, we demonstrate time-resolved photoelectron circular dichroism (TRPECD) with ultrashort circularly polarized vacuum-ultraviolet (VUV) pulses from a tabletop source. We demonstrate the capabilities of VUV-TRPECD by resolving the chirality changes in time during the photodissociation of atomic iodine from two chiral molecules. We identify several general key features of TRPECD, which include the ability to probe dynamical chirality along the complete photochemical reaction path, the sensitivity to the local chirality of the evolving scattering potential, and the influence of electron scattering off dissociating photofragments. Our results are interpreted by comparison with high-level ab-initio calculations of transient PECDs from molecular photoionization calculations. Our experimental and theoretical techniques define a general approach to femtochirality.

Time-Evolving Chirality Loss in Molecular Photodissociation Monitored by X-ray Circular Dichroism Spectroscopy

“…7 Similarly, the 2-butyl radical racemization, induced by a 60 fs umbrella mode, was observed recently. 16 We thus expect that the inclusion of out-of-plane mode will make the observed TRXCD signals decay by the time with positive/negative oscillations.…”

“…The out-of-plane bending of the CHO group is responsible for the positive/negative oscillatory pattern with a 120 fs period in our previous work on formamide . Similarly, the 2-butyl radical racemization, induced by a 60 fs umbrella mode, was observed recently . We thus expect that the inclusion of out-of-plane mode will make the observed TRXCD signals decay by the time with positive/negative oscillations.…”

“…Thus, it is indirectly sensitive to nuclear dynamics with a not straightforward assignment of the electronic changes. The time-resolved photoelectron CD measurements of neutral 2-iodobutane from the same group reported rapid decay within 60 fs, accounting for the rapid racemization of nascent 2-butyl radicals …”

The ultrafast vibronic dynamics of ammonia's D̃ state

“…These sources have proven to be indispensible tools for studies of electronic dynamics, allowing access to high-lying electronic states as a pump, or light-induced dynamics leading to photoproducts in the electronic ground state as a probe. [30][31][32][33][34][35][36][37][38] Presented here, the high-lying Rydberg states of ammonia are revisited from previous work. 39 Making use of improved energy resolution, greater detail can be extracted, providing a far more complete description of the light-induced dynamics in these states of ammonia.…”

“…These sources have proven to be indispensible tools for studies of electronic dynamics, allowing access to high-lying electronic states as a pump, or light-induced dynamics leading to photoproducts in the electronic ground state as a probe. 30–38…”