Attosecond photoionization delays in the vicinity of molecular Feshbach resonances

Abstract

Temporal delays extracted from photoionization phases are currently determined with attosecond resolution by using interferometric methods. Such methods require special care when photoionization occurs near Feshbach resonances due to the interference between direct ionization and autoionization. Although theory can accurately handle these interferences in atoms, in molecules, it has to face an additional, so far insurmountable problem: Autoionization is slow, and nuclei move substantially while it happens, i.e., electronic and nuclear motions are coupled. Here, we present a theoretical framework to account for this effect and apply it to evaluate time-resolved and vibrationally resolved photoelectron spectra and photoionization phases of N 2 irradiated by a combination of an extreme ultraviolet (XUV) attosecond pulse train and an infrared pulse. We show that Feshbach resonances lead to unusual non–Franck-Condon vibrational progressions and to ionization phases that strongly vary with photoelectron energy irrespective of the vibrational state of the remaining molecular cation.

Open questions in attochemistry

“…Inclusion of nuclear motion to describe the evolution of the electronic wave packet as well as an explicit evaluation of the experimental observables, namely time-resolved photoelectron and photo-ion spectra, is the necessary complement to the above-mentioned experimental efforts. A good example of this has recently been reported for the case of the nitrogen molecule 15 .…”

Understanding attosecond streaking

“…Those very same issues are also relevant in the interpretation of delays obtained in Reconstruction of Attosecond Beating By Interference of Two-photon transitions (RABBIT) [52,55,56], a technique based on interferometry that also aims at measuring ionization delays by applying an XUV and IR pulse. RABBIT has also been widely applied to atoms, molecules, liquids and solids [57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72] and has been shown to give results that are equivalent to those obtained by attosecond streaking [9,61,73,74]. In RABBIT experiments the CLC is often referred to as continuum-continuum coupling (usually abbreviated as CC) but describes the same effect [9,39,65,73].…”

Resonant Photoionization of CO2 up to the Fourth Ionization Threshold

“…The development of attosecond VUV/XUV pulses has opened new doorways for imaging and steering electron dynamics in many-electron systems, in particular, molecular systems. − Recent examples also include retrieving real-space movies of the internal motion in molecules, , monitoring the birth of a photoelectron in helium, extracting photoionization time delays of molecules in the vicinity of shape and Feshbach resonances, ,,− and the observation of correlation-driven charge migration in a DNA building block . The use of these light sources usually leads to ionization, where in addition to the photoelectron ejection, other processes involving two or more electrons can also take place, e.g., autoionization of Feshbach resonances, ionization leaving the remaining ion in an excited state (shakeup), inner-shell ionization followed by Auger decay, and Auger decay combined with shakeup.…”