Enantioselective fragmentation of an achiral molecule in a strong laser field
The investigation of the interaction between a chiral molecule and chiral light is of great interest. The goal of the research is not only the fundamental understanding of the process but also a sensitive analysis method for the investigation of chiral systems and enantioselective control of chemical reactions with light. We report on an enantioselective fragmentation of formic acid where the observed enantiomer strongly depends on the orientation of the molecule with respect to the laser propagation direction and the helicity of the ionizing light.
Fig. 1 shows the dependency of the observed enantiomer on the orientation of the molecule in the molecular system. If the laser impacts on the molecule from a direction where the color-coded sphere is yellow (blue), we observe the R (S)-enantiomer.
The dependency of the differential photoion circular dichroism is depicted in Fig. 2 displaying strong PICD signals up to 20%. For the mirror image molecule, the PICD signal inverts its sign. The PICD is a sensitive probe for the molecular structure (Fig. 3). Gating on different angles on which the proton attached to the carbon atom is bend out of the O-C=O plane, the PICD pattern changes.
Figure 1:The colored sphere indicates the observed enantiomer from the five-body fragmentation of formic acid (center). Impacts the laser the molecule from a side, where the sphere is yellow, the R-enantiomer is observed, the S-enantiomer is observed if the laser hits the molecule from a side, where the sphere is blue.
Figure 2: Differential PICD of formic acid for the R-enantiomer (left) and the S-enantiomer (right). The PICD is calculated as PICD=(N_RCP-N_CLP)/(N_RCP-N_CLP ), and thus indicates the difference in the ionisation probability between left and right handed circularly polarized light. For the mirror image molecule, the PICD inverts its sign.
Figure 3: PICD of R-formic acid with gate on different angles cos(α), the angle on which the proton attached to the carbon atom is bend out of the O-C=O plane. The changes in the PICD pattern and strength demonstrate the usability of PICD as probe for the molecular structure.