Circular dichroism in the photoelectron angular distribution.Conformers of free chiral molecules in gas phase

Chiral recognition plays a central role in the development of enantioselective systems as specific reaction for catalysis or drug delivery. The state of the art spectroscopy that gave rise to the development of stereochemistry is Natural Circular Dichroism (NCD) in the wavelength interval ranging from IR to UV. The extension of NCD to the VUV - X ray range had to wait for third generation synchrotron radiation insertion device devoted to the production of circular polarized light. In this wavelength range it has been possible to explore the natural circular dichroism in valence photoemission [1]; circular polarized light is the basis to couple the information of the molecular electronic states with the chiral properties. For the first time the NCD spectroscopy has been successfully applied to resolve the conformational population of enantiomers in gas phase. We have studied in the last few years several chiral compounds: rigid and ring systems such as methyl-oxirane [2,3,4] and 3-hydroxy tetrahydrofurane [5], linear and flexible compound such as alaninol (2-amino-1-propanol) and isopropanolamine (1-amino-2-propanol) [6]. In particular in the trend of the dichroism as a function of the kinetic energy of the photoelectrons it has been possible not only to explain the dependence of the dichroism from the electronic and structural properties of the chiral systems, but also to point out how the circular dichroism can be sensitive to the conformational structural changing.