Enantioselective One-Photon Excitation of Formic Acid

We use one-photon excitation to promote K-shell electrons of formic acid (which has a planar equilibrium structure) to an antibonding π^{*} orbital. The excited molecule is known to have a (chiral) pyramidal equilibrium structure. In our experiment, we determine the handedness of the excited molecule by imaging the momenta of charged fragments, which occur after its Coulomb explosion triggered by Auger-Meitner decay cascades succeeding the excitation. We find that the handedness of the excited molecule depends on its spatial orientation with respect to the propagation (or polarization) direction of the exciting photon. The effect is largely independent of the exact polarization properties of the light driving the 1s→π^{*} excitation.