Angle-resolved photoelectron spectroscopy of randomly oriented 3-hydroxytetrahydrofuran enantiomers

Circular dichroism in the angular distribution of valence photoelectrons emitted from randomly oriented 3-hydroxytetrahydrofuran enantiomers (Th-S and Th-R) has been observed in gas-phase experiments using circularly polarized vacuum ultraviolet (VUV) light. The measured dichroism for both Th-S and Th-R, acquired at the single magic angle theta=234.73 degrees and at photon energies of 22, 19, 16, and 14 eV, points to an asymmetric forward-backward scattering of the photoelectrons from their highest occupied molecular orbitals (HOMO) HOMO-1 and HOMO-2, of up to 5%, depending on the photon energy. The asymmetry reverses on exchange of either the helicity of the radiation or the configuration of Th. The photoionization dichroic D parameters of Th-S and Th-R have been measured and their values discussed in the light of LCAO B-spline density functional theory (DFT) predictions. While an acceptable agreement is found between the dichroic parameter measured and calculated at the highest photon energy for the HOMO and HOMO-2 orbitals of Th, a significant discrepancy is observed for the HOMO-1 state which is attributed to the floppiness of Th, in particular to the comparatively large sensitivity of the size and shape of its HOMO-1 on nuclear vibrational motion.