A photoionization investigation of small, homochiral clusters of glycidol using circularly polarized radiation and velocity map electron–ion coincidence imaging

Abstract

A detailed study of the valence photoionization of small homochiral glycidol (C3O2H6) clusters is carried out with the help of circularly-polarized VUV synchrotron radiation by recording photoionization-based spectroscopic data detected by velocity map electron imaging with coincidence ion selection. We show that information on the stability of cationic as well as neutral chiral clusters can be obtained with enhanced sensitivity by examining the chiral fingerprint encapsulated in Photoelectron Circular Dichroism (PECD) spectra. In particular, by varying the clustering conditions we demonstrate that the PECD signal effectively carries the signature of the neutral precursor species, prior to any fragmentation of the ion, as may be inferred from the below-threshold monomer measurements (including ion imaging). Here the monomer's direct ionization channel is closed and the monomer ion hence must result exclusively as a fragment from dissociative ionization of the dimer (or higher) clusters. At higher photon energies, the mass-selection on the electron spectroscopy data, achieved through filtering the electron images in coincidence with selected ion masses, evidently succeeds in providing a degree of size-selection on the neutral clusters being ionized with, in particular, a clear differentiation of monomer and dimer PECD, showing the strong sensitivity of this chiroptical effect to the non-local long-range molecular potential.

Chiral Asymmetry in the Multiphoton Ionization of Methyloxirane Using Femtosecond Electron–Ion Coincidence Imaging

“…This inherent sensitivity, combined with the in-built experimental efficiency of charged particle detection, make PECD an ideal method to probe isolated chiral molecules in the gas phase, which can even be extended to observe minor cluster components generated in a supersonic molecular beam. 10 In the present context it is then no surprise that methyloxirane has been widely investigated, both experimentally 11−14 and theoretically, 11,14−16 by PECD. Vibrationally resolved PECD measurements have lately revealed an inversion of the chiral electron scattering asymmetry caused by weakly excited normal mode vibrations, 17 highlighting the significance of complete vibronic treatments for fully understanding the chirality displayed by this molecule.…”

Observation of Photoelectron Circular Dichroism Using a Nanosecond Laser

“…[5] This effect arises in the electric dipole approximation and was first observed experimentally using single-photon ionization. [6] The forward-backward asymmetry is known as photoelectron circular dichroism [7] (PECD) and typically exhibits large magnitudes with experimental values as high as 37 %. [8] The origin of PECD lies in the quantum interference of outgoing partial waves.…”

“…[9] As PECD has been observed for single-photon ionization out of an achiral core-shell orbital, it has been interpreted as being mainly a final state effect. [7,10] Measuring PECD has been boosted by techniques capturing the full photoelectron momentum distribution such as velocity map imaging (VMI) [11] or a recently developed stereo-electron detector. [12] Recently, single-photon PECD [13,14] highlighting in addition the relevance for astrophysical research [15] has been reviewed.Note that ionization with a single photon is independent on the temporal structure of the light.…”

Relaxation Dynamics in Photoexcited Chiral Molecules Studied by Time-Resolved Photoelectron Circular Dichroism: Toward Chiral Femtochemistry

“…This shows that the phases of partial wave functions can be determined by their values far from the ionic core and that PECD is thus a very long-range probe of the whole molecular potential, as already observed in one-photon PECD, for instance in clusters. 23,24 At the same time, by using a pump step, partial alignment is achieved, and when a Rydberg state is excited, a smaller number of angular momentum components are required to describe the photoelectron continuum. It would be interesting to investigate these two latter conditions to determine their respective impact on the large asymmetry that is observed here.…”