Pump-probe spectroscopy of chiral vibrational dynamics. 

Abstract

A planar molecule may become chiral upon excitation of an out-of-plane vibration, changing 
its handedness during half a vibrational period. When exciting such a vibration in an 
ensemble of randomly oriented molecules with an infrared laser, half of the molecules will 
undergo the vibration phase-shifted by p compared to the other half, and no net chiral signal 
is observed. This symmetry can be broken by exciting the vibrational motion with a Raman 
transition in the presence of a static electric field. Subsequent ionization of the vibrating 
molecules by an extreme ultraviolet pulse probes the time-dependent net handedness via the 
photoelectron circular dichroism. Our proposal for pump-probe spectroscopy of molecular 
chirality, based on quantum-chemical theory and discussed for the example of the carbonyl 
chlorofluoride molecule, is feasible with current experimental technology. Planar molecules 
can be made chiral with electric fields only, and a net chiral signature can be recorded upon 
ionization.