Chiral signatures in angle-resolved valence photoelectron spectroscopy of pure glycidol enantiomers

Abstract

Photoionization of the chiral molecule glycidol has been investigated in the valence region. Photoelectron circular dichroism (PECD) curves have been obtained at various photon energies by using circularly polarized VUV synchrotron radiation and a velocity map imaging technique to record angle-resolved photoelectron spectra (PES). The measured chiral asymmetries vary dramatically with the photon energy as well as with the ionized orbital, improving the effective orbital resolution of the PECD spectrum with respect to the PES. Typical asymmetry factors of 5% are observed, but the peak values measured range up to 15%. The experimental results are interpreted by continuum multiple scattering (CMS-Xalpha) calculations for several thermally accessible glycidol conformers. We find that a nearly quantitative agreement between theory and experiments can be achieved for the ionization of several molecular orbitals. Owing to the sensitivity of PECD to molecular conformation this allows us to identify the dominant conformer. The influence of intramolecular hydrogen bond orbital polarization is found to play a small yet significant role in determining the chiral asymmetry in the electron angular distributions.

Determination of accurate electron chiral asymmetries in fenchone and camphor in the VUV range: sensitivity to isomerism and enantiomeric purity

“…In the higher resolution PES recorded by Rennie et al 51 with a hemispherical analyzer the electronic band structure is slightly more marked and seen to correlate with the PECD changes. The OVGF calculations published by Rennie et al also correspond to the observed oscillations, which highlights the enhanced sensitivity of PECD to electronic structure when compared to usual observables such as ionization cross--sections -even in the case of congested electronic bands as already observed in camphor 36 and glycidol 13 .…”

Identifying and Understanding Strong Vibronic Interaction Effects Observed in the Asymmetry of Chiral Molecule Photoelectron Angular Distributions

“…We comment that a general advantage of PECD has been shown in its ability to reveal underlying orbital electronic structure even in spectrally congested regions where individual orbitals are not resolved in the PES. [39,[47][48][49] This arises because there may often be large variations in b 1 (in magnitude and sign) between adjacent orbitals even while the cross sections are quite commensurate -with consequently little distinguishable variation in intensity of the regular spectrum. In a somewhat similar manner, PECD may here provide clues to the position of vibrational transitions, even when these are too weak and the resolution insufficient, to show as significant structure in the PES alone.…”

Photoelectron circular dichroism: Chiral asymmetry in the angular distribution of electrons emitted by (+)‐S‐carvone

“…The combination of energy and angular measurement of the photoelectrons provides for PECD phenomena to be resolved into contributions made by individual initial orbitals. 8,9,11 The exceptional size of PECD asymmetry factors, several orders of magnitude greater than typically encountered in normal CD measurements made with isolated molecules (i.e., in the absence of cooperative condensed phase enhancement mechanisms) suggests that high sensitivities are potentially achievable. However, it should be stressed that this arises from the ability of the technique to provide angular resolution of the final state wave function.…”

“…The first fully realistic calculations suggested that asymmetry factors of the order of a few 10% should be expected, a prediction which has subsequently been borne out by experiment in a number of different molecules. [2][3][4][5][6][7][8][9][10][11] As a form of photoelectron spectroscopy, PECD is naturally performed under vacuum conditions using vapour phase samples of randomly oriented molecules; either at low pressure ( 5 3 10 25 mbar) in a gas cell or effusive jet, or in a supersonic molecular beam in the spectrometer interaction region. In either case the sample molecules are effectively isolated, noninteracting and nonsolvated.…”