Molecular frame photoemission time delay*

The time delay in one-photon emission is given by the energy derivative of the phase of the transition matrix element for the process. In molecular systems, the transition matrix element depends on the emission direction, relative to the orientation of the molecule, i.e. in the molecular frame, and on the polarization direction of the radiation.  As a consequence, the time delay can have a complicated direction dependence in the molecular frame.   The molecular frame photoemission time delay provides insights into the attosecond dynamics induced by one-photon absorption, including the role of continuum resonant states, hole localization, and diffractive scattering. Here, we report the angular dependence of single-photon ionization delays across a shape resonance in the photoionization of NO [1] studied both in theory and experiment. The angle-dependent time delay variations of a few hundreds of attoseconds, resulting from the interference of the resonant and non-resonant contributions to the dynamics of the ejected electron, are well described using a multichannel Fano model where the time delay of the resonant component is angle-independent. A theoretical study of the photoionization of Kr₂ shows the effect of both hole localization and diffractive scattering on molecular-frame time delays, which are related to experimental laboratory-frame measurements [2]. Additionally, we consider the behavior of the photoemission time delay in molecular photodetachment.  In this case, the absence of the long-range Coulomb interaction in the resulting electron-neutral molecule scattering yields more detailed information about the low-energy photoemission dynamics. A theoretical study of the detachment from core levels of CN^– shows that the asymmetry of the system can lead to strong molecular frame dependence in the resulting photoemission time delays at low energies.

[1] F. Holzmeier, J. Joseph, J. C. Houver, M. Lebech, D. Dowek, and R. R. Lucchese, Nature Communications 12, 7343 (2021).

[2] S. Heck, M. Han, D. Jelovina, J.-B. Ji, C. Perry, X. Gong, R. Lucchese, K. Ueda, and H. J. Wörner, Phys. Rev. Lett. 129, 133002 (2022).