Femtosecond gas-phase mega-electron-volt ultrafast electron diffraction

Area of Science:

• Chemical Physics
• Molecular Dynamics
• Spectroscopy

Background:

• Ultrafast electron diffraction (UED) with nonrelativistic electrons allows atomic-scale molecular structure determination.
• Achieving picosecond temporal resolution has been a barrier to observing gas-phase chemical reactions in real-time.
• Molecular movies require high spatial and temporal resolution to visualize dynamic processes.

Purpose of the Study:

• To present the design of a new mega-electron-volt (MeV) UED apparatus at SLAC National Accelerator Laboratory.
• To enable real-time imaging of ultrafast structural dynamics in gas-phase molecules.
• To overcome the temporal resolution limitations of previous UED techniques.

Main Methods:

• Development of a gas-phase MeV UED apparatus utilizing high-energy electrons.
• Implementation of a compact differential pump section for enhanced vacuum isolation.
• Systematic characterization of spatial resolution, temporal resolution, and long-term stability.

Main Results:

• Achieved 65 fs root mean square temporal resolution.
• Attained 0.63 Å spatial resolution and 0.22 Å^-1 reciprocal-space resolution.
• Successfully captured real-time molecular movies of photochemical mechanisms like bond breaking and conical intersection crossings.

Conclusions:

• The SLAC gas-phase MeV UED apparatus provides unprecedented spatial-temporal resolution for molecular dynamics studies.
• The compact design facilitates high vacuum conditions crucial for gas-phase experiments.
• This technology opens new avenues for investigating fundamental chemical processes in real-time.