Abstract
A shape resonance emerges during the light absorption in many molecules with a gigantic burst amplitude and a lifetime of hundreds of attoseconds. Recent advances in attosecond metrology revealed the attosecond lifetime of the shape resonance. For a heteronuclear molecule, the asymmetric initial state and landscape of the molecular potential would lead to an asymmetric shape resonance, whose effect, however, has not been characterized yet. Here, we employ an attosecond interferometer to investigate the molecular-frame photoionization time delay in the vicinity of the shape resonance of the NO molecule. Driven by photons with energy ranging from 23.8 eV to 36.5 eV, a 150 attosecond difference in the time delay is observed between photoemission from the end. Our quantum scattering theoretical simulations reproduce well our experimental findings. It illustrates that the asymmetric time delay originates from the interference between resonant and nonresonant photoionization pathways.
- Received 15 April 2021
- Accepted 8 November 2021
DOI:https://doi.org/10.1103/PhysRevX.12.011002
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
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.
