Femtosecond response of polyatomic molecules to ultra-intense hard X-rays

Area of Science:

• Atomic and Molecular Physics
• Ultrafast Science
• X-ray Science

Background:

• X-ray free-electron lasers (XFELs) probe matter under extreme conditions.
• High-intensity X-rays cause significant atomic ionization.
• Current understanding suggests molecular ionization mirrors isolated atom behavior.

Purpose of the Study:

• Investigate the femtosecond response of molecules with heavy atoms to ultra-intense hard X-ray pulses.
• Determine if molecular ionization under these conditions differs from isolated atom ionization.
• Develop accurate models for X-ray-driven processes in complex systems.

Main Methods:

• Experimental irradiation of small polyatomic molecules containing a heavy atom with ultra-intense (10^20 W/cm^2), hard X-ray (8.3 keV) pulses.
• Detailed computational modeling of the molecular response.
• Analysis of electron emission and charge dynamics.

Main Results:

• Molecular ionization is significantly enhanced compared to isolated heavy atoms under ultra-intense hard X-ray irradiation.
• Ultrafast intramolecular charge transfer refills core holes, enabling further inner-shell ionization.
• Molecules emit over 50 electrons during the X-ray pulse, indicating a dramatically different ionization pathway.

Conclusions:

• The response of molecules to ultra-intense hard X-rays is qualitatively different from that of isolated atoms.
• Intramolecular charge transfer plays a crucial role in enhancing ionization.
• Efficient modeling of X-ray-driven processes in complex systems at ultrahigh intensities is achievable.