Charge-induced chemical dynamics in glycine probed with time-resolved Auger electron spectroscopy

Abstract

In the present contribution, we use x-rays to monitor charge-induced chemical dynamics in the photoionized amino acid glycine with femtosecond time resolution. The outgoing photoelectron leaves behind the cation in a coherent superposition of quantum mechanical eigenstates. Delayed x-ray pulses track the induced coherence through resonant x-ray absorption that induces Auger decay. Temporal modulation of the Auger electron signal correlated with specific ions is observed, which is governed by the initial electronic coherence and subsequent vibronic coupling to nuclear degrees of freedom. In the time-resolved x-ray absorption measurement, we monitor the time-frequency spectra of the resulting many-body quantum wave packets for a period of 175 fs along different reaction coordinates. Our experiment proves that by measuring specific fragments associated with the glycine dication as a function of the pump-probe delay, one can selectively probe electronic coherences at early times associated with a few distinguishable components of the broad electronic wave packet created initially by the pump pulse in the cation. The corresponding coherent superpositions formed by subsets of electronic eigenstates and evolving along parallel dynamical pathways show different phases and time periods in the range of [Formula: see text] and [Formula: see text] fs. Furthermore, for long delays, the data allow us to pinpoint the driving vibrational modes of chemical dynamics mediating charge-induced bond cleavage along different reaction coordinates.

Coupled Electron–Nuclear Dynamics Induced and Monitored with Femtosecond Soft X-ray Pulses in the Amino Acid Glycine

“…This scenario leads to a strong signal enhancement because the total transition dipole moment is maximized. In the further course of the wave packet propagation, the electronic coherence is lost, and the dynamics of the quantum system is exclusively governed by nuclear motion in the R coordinate until vibrational relaxation dissipates the excitation energy among the 3 M –6 nuclear degrees of freedom or molecular fragmentation sets in ref ( 20 ).…”

Advances in modeling attosecond electron dynamics in molecular photoionization

“…65 Most importantly, the methodology can be applied to the simulation of complete numerical pump-probe experiments of ultrafast dynamics in molecular systems. [65][66][67] This is because the hierarchies of both ADC and RCS-ADC methods extend across different ionization stages, thus allowing the simulation of the interaction of the cation with yet another ionizing laser pulse probing its dynamics. The ab initio simulations of the interaction between the molecular systems and the pump and probe laser pulses are performed by solving the TD Schrödinger for the neutral system and the von Neumann equation…”

“…In, Reference [66] an x-ray pump pulse is used to photo-ionize the molecular Glycine I conformer (Gly I) and a second time-delayed, identical x-ray pulse is used to probe the quantum-coherent electron dynamics triggered in the Gly I cation by the pump by looking at the timedelay dependent photoelectron yield. The photon energy of the probe (and pump) pulse was tuned to 274 eV, 66,67 that is, just below the C K-edge.…”

“…Most importantly, the methodology can be applied to the simulation of complete numerical pump‐probe experiments of ultrafast dynamics in molecular systems 65–67 . This is because the hierarchies of both ADC and RCS‐ADC methods extend across different ionization stages, thus allowing the simulation of the interaction of the cation with yet another ionizing laser pulse probing its dynamics.…”