Isolating Attosecond Electron Dynamics in Molecules where Nuclei Move Fast.

Laura Cattaneo,Roger Y Bello,Luca Pedrelli,Alicia Palacios,Phillip D Keathley,Fernando Martín,Ursula Keller

doi:10.1103/physrevlett.128.063001

Abstract

Capturing electronic dynamics in real time has been the ultimate goal of attosecond science since its beginning. While for atomic targets the existing measurement techniques have been thoroughly validated, in molecules there are open questions due to the inevitable copresence of moving nuclei, which are not always mere spectators of the phototriggered electron dynamics. Previous work has shown that not only can nuclear motion affect the way electrons move in a molecule, but it can also lead to contradictory interpretations depending on the chosen experimental approach. In this Letter we investigate how nuclear motion affects and eventually distorts the electronic dynamics measured by using two of the most popular attosecond techniques, reconstruction of attosecond beating by interference of two-photon transitions and attosecond streaking. Both methods are employed, in combination with abinitio theoretical calculations, to retrieve photoionization delays in the dissociative ionization of H_{2}, H_{2}→H^{+}+H+e^{-}, in the region of the Q_{1} series of autoionizing states, where nuclear motion plays a prominent role. We find that the experimental reconstruction of attosecond beating by interference of two-photon transitions results are very sensitive to bond softening around the Q_{1} threshold (27.8eV), even at relatively low infrared (IR) intensity (I_{0}∼1.4×10^{11} W/cm^{2}), due to the long duration of the probe pulse that is inherent to this technique. Streaking, on the other hand, seems to be a better choice to isolate attosecond electron dynamics, since shorter pulses can be used, thus reducing the role of bond softening. This conclusion is supported by very good agreement between our streaking measurements and the results of accurate theoretical calculations. Additionally, the streaking technique offers the necessary energy resolution to accurately retrieve the fast-oscillating phase of the photoionization matrix elements, an essential requirement for extending this technique to even more complicated molecular targets.

Highlights

Isolating Attosecond Electron Dynamics in Molecules where Nuclei Move FastLaura Cattaneo,1,*,† Luca Pedrelli ,1,† Roger Y
Capturing electronic dynamics in real time has been the ultimate goal of attosecond science since its beginning
Previous work has shown that can nuclear motion affect the way electrons move in a molecule, but it can lead to contradictory interpretations depending on the chosen experimental approach

Summary

Isolating Attosecond Electron Dynamics in Molecules where Nuclei Move Fast

Laura Cattaneo,1,*,† Luca Pedrelli ,1,† Roger Y. In this Letter we investigate how nuclear motion affects and eventually distorts the electronic dynamics measured by using two of the most popular attosecond techniques, reconstruction of attosecond beating by interference of two-photon transitions and attosecond streaking. Both methods are employed, in combination with ab initio theoretical calculations, to retrieve photoionization delays in the dissociative ionization of H2, H2 → Hþ þ H þ e−, in the region of the Q1 series of autoionizing states, where nuclear motion plays a prominent role. Exposing molecular targets to such long NIR pulses can trigger nuclear dynamics that contaminate the electron dynamics of interest Another method that has been widely used to obtain photoionization time delays in atomic systems is attosecond streaking [4].

Published by the American Physical Society

Photoionization channel

Findings

ACDC reconstruction