Time Delays in Photodetachment of Atomic and Molecular Anions at Low Energies

Photoionization time delays have attracted both theoretical and experimental

attention in the last decade since the delays contain information about the structure and dynamics

of the atomic and molecular systems. However, in the case of photoionization of neutral species,

the Coulomb interaction between the outgoing photoelectron and residual cation dominates the

dynamics and obscures the electron correlation and polarization effects at low energies (below 5-10 eV).

In the case of the photodetachment of anions, the outgoing photoelectron interacts with a neutral atom or molecule

and the correlation and polarization dominate the dynamics at low energies. Due to the high

polarizability of lithium, the time delay goes to 1.7 fs and 0.5 fs at the threshold for the

valence and core photodetachment of lithium anion, respectively. The dynamics is even more interesting

in the case of molecular anions that have low-lying shape resonances. Recently, we have studied

the core photodetachment of C2^- and CN^-, where we calculated large time delays (up to 4 fs) with dramatic

assymetries in the molecular frame [1].

To our knowledge there have been almost no experimental results in the case of photodetachment due to

the challenges connected with the preparation of the anions and measuring time delays at low photoelectron energies.

In this theoretical contribution, we address the measurement problems associated with the low-energy region to stimulate the experimental effort.

We discuss our preliminary results of time-dependent photodetachment calculations using the R-matrix method [2] adopting

the pump-probe scheme of the convential and angular kinetic energy streaking with realistic XUV and IR pulses.

References:

[1] Rescigno et al, Phys. Rev. A 110, 013122 (2024).

[2] Brown A. C. et al., Comput. Phys. Commun. 250, 107062 (2020).