Femtosecond - Coincidence Studies of Molecular Chirality

• Applicant: Professor Dr. Karl-Michael Weitzel
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 345790396

• Final Report Year: 2021

Final Report Abstract

Over the last two decades or so we have witnessed significant progress in the analysis of molecular chirality by optical methods. This project is focused on two chiroptical techniques based on laser ionization. The first is the Photo Ion Circular Dichroism (PICD), the second is the Photo Electron Circular Dichroism (PECD). While the PICD is obtained as the difference of total (angle integrated), mass-selected ion yields, the PECD is obtained from the difference in the angular distribution of photoelectrons measured in the forward and backward direction relative to the laser beam direction. The PICD is in general dominated by magnetic contributions to the total dipole transition moment. In contrast to that, the PECD arises from pure electrical dipole transition moments. Up to the beginning of this project reports on optical chirality analysis either exclusively focused on PICD or on PECD measurements. The goal of this project was to conduct the first true coincident measurement of PICD and PECD and finding an answer to the question whether PICD and PECD can both be different from zero for the same ionization process. The pivotal result of the project is that indeed both PICD and PECD can be different from zero at the same time. We present one example where PICD and PECD have the same sign and basically go hand in hand (methyloxirane). We present another example where PICD and PECD have different sign, not only exhibiting a sign change between PICD and PECD for all ions but also exhibiting a sign change between the parent ion and the dominant fragment ions (1-phenylethylamine) for both PICD and PECD. Thus the PICD and PECD are concluded to be indeed complimentary and as a consequence it would be best to have the possibility to measure both quantities in order to achieve the optimum sensitivity to the distinction of molecular chirality.

Publications

• (2020): Coincident measurement of photo-ion circular dichroism and photo-electron circular dichroism. In: Phys. Chem. Chem. Phys. 22 (24), p. 13707–13712
  Lehmann, C.S.; Weitzel, K.-M.
  
• (2021): Photoelectron Circular Dichroism in the Photodetachment of Amino Acid Anions. In: Angewandte Chemie (International ed. in English) 60 (33), p. 17861–17865
  Krüger, P.; Weitzel, K.-M.