Angle-dependent strong-field ionization of halomethanes

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Molecular Physics

Background:

• Strong-field ionization (SFI) is crucial for understanding molecular response to intense laser fields.
• Controlling charge migration dynamics is key for attosecond science and molecular electronics.
• Halogenated methanes (halomethanes) offer a tunable platform to study ionization processes.

Purpose of the Study:

• To experimentally and theoretically investigate the angle-dependent strong-field ionization (SFI) of chloromethane (CH3Cl) and bromomethane (CH3Br).
• To elucidate the underlying mechanisms causing differences in ionization yields between these molecules.
• To establish trends in ionization dynamics with increasing halogen mass.

Main Methods:

• Experimental: Two-color pump-probe spectroscopy using intense, linearly polarized 800 nm laser pulses to induce and probe rotational wave packets.
• Theoretical: Time-dependent density functional theory (TD-DFT) calculations of angle-dependent SFI yields.
• Data Analysis: Fitting experimental data to extract angle-dependent ionization yields.

Main Results:

• Good agreement was achieved between experimental measurements and theoretical calculations for both CH3Cl and CH3Br.
• A significant difference in angle-dependent ionization yields was observed between CH3Cl and CH3Br.
• Calculations indicated that multichannel ionization in CH3Cl and increased hole localization on Br in CH3Br contribute to these differences.

Conclusions:

• The ionization dynamics of halomethanes are sensitive to the type of halogen atom, influencing multichannel vs. single-channel ionization and hole localization.
• Trends in ionization dynamics can be discerned by varying the halogen mass (e.g., including CH3F).
• Molecular alignment and chemical functionalization are critical for controlling charge migration initiated by SFI.