Imaging intramolecular hydrogen migration with time- and momentum-resolved photoelectron diffraction

Area of Science:

• Chemical Physics
• Ultrafast Spectroscopy
• Molecular Dynamics

Background:

• Imaging ultrafast hydrogen migration is difficult due to hydrogen's light mass and low scattering cross-section.
• Existing ultrafast spectroscopy methods face limitations in resolving rapid hydrogen atom movement.

Purpose of the Study:

• To introduce time- and momentum-resolved photoelectron diffraction (TMR-PED) as a novel technique for ultrafast hydrogen migration imaging.
• To demonstrate the capability of TMR-PED in visualizing hydrogen dynamics in the ethanol molecule.

Main Methods:

• Combining molecular dynamics and electron scattering theoretical methods.
• Utilizing time- and momentum-resolved photoelectron diffraction (TMR-PED).
• Employing multi-coincidence detection with a carefully chosen reference frame.

Main Results:

• TMR-PED successfully imaged single and double hydrogen migration in doubly-charged ethanol with few-femtosecond and angstrom resolutions.
• The technique provided insights into proton extraction following H2 roaming.
• Hydrogen dynamics were visualized as distinct moving features in polarization-averaged molecular-frame photoelectron angular distributions (PA-MFPADs).

Conclusions:

• TMR-PED offers a powerful approach to overcome limitations in studying ultrafast hydrogen migration.
• The method allows for direct, high-resolution imaging of hydrogen dynamics from initiation to completion.
• This technique provides a straightforward visualization of complex molecular events like hydrogen migration and proton extraction.