Lawrence Berkeley National Laboratory

Photoemission, in which photons cause atoms or molecules to emit electrons, is not an instantaneous process. The emitted electron may take hundreds of attoseconds to traverse the local potential of its parent atom or molecule after photoabsorption. The exact time is sensitive to the potential landscape the electron encounters, which causes a delay in when the photoelectron’s wave packet emerges from different parts of the molecule. Here, we experimentally explore this delay in the hitherto elusive frame of reference of the molecule, which allows us to observe photoelectron emission relative to specific orientations of the molecule.As a prototype process, we choose the photoionization of the inner valence electron of the NO molecule. During the photoelectron’s excursion, it experiences an asymmetric molecular potential landscape and a dynamical centrifugal potential. We introduce an approach to clock the photoionization dynamics of the NO molecule in its molecular frame. A key finding is an asymmetric photoemission delay difference, around 150 attoseconds, at the opposite ends of the molecule. Our theoretical simulation illustrates that the asymmetric delay originates from the interference between multiple photoionization pathways.Despite being demonstrated in a heteronuclear diatomic molecule, our methods and findings are applicable to the photoemission dynamics in many molecules, surfaces, and interfaces with asymmetric potentials. Our approach opens a new avenue for exploring the attosecond photoelectron dynamics in complex systems and investigating the time-resolved quantum dynamics in solutions, complex materials, and biologic tissues.