Attosecond X-ray Diffraction Triggered by Core or Valence Ionization of a Dipeptide

Area of Science:

• Chemical Physics
• Molecular Dynamics
• Ultrafast Spectroscopy

Background:

• Advancements in intense ultrafast X-ray sources enable real-time, real-space observation of electronic dynamics.
• Time-resolved X-ray diffraction is a powerful technique for visualizing molecular processes.
• Understanding electronic dynamics is crucial for controlling chemical reactions and molecular functions.

Purpose of the Study:

• To simulate and analyze electronic dynamics in the glycine-phenylalanine (GF) dipeptide after core or valence ionization.
• To investigate charge migration pathways and timescales within the dipeptide.
• To explore the potential of attosecond X-ray diffraction for real-space charge density imaging.

Main Methods:

• Real-time time-dependent density functional theory (RT-TDDFT) simulations.
• Calculation of time-evolving dipole moment, charge density, and X-ray diffraction signals.
• Analysis of charge oscillation timescales and Fourier transforms of dipole moments.

Main Results:

• Simulated charge oscillation timescales of 7 fs for valence ionization and 500 as for core ionization in the GF dipeptide.
• Identified charge migration mediated by delocalized lone-pair orbitals of the amide group.
• Demonstrated that heterodyne-detected attosecond X-ray diffraction can yield real-space charge density.

Conclusions:

• RT-TDDFT simulations provide detailed insights into ultrafast electronic dynamics in peptides.
• The glycine chain influences charge oscillation timescales compared to smaller molecules.
• Attosecond X-ray diffraction holds promise for mapping electronic charge distributions in real space.