Delving into multiple ionization of nitromethane using ω/2ω fs laser fields

Area of Science:

• Physical Chemistry
• Atomic, Molecular, and Optical Physics
• Quantum Dynamics

Background:

• Understanding molecular ionization dynamics under intense laser fields is crucial for controlling chemical reactions.
• Nitromethane (CH3NO2) presents a complex system for studying multiple ionization due to its isomers and functional groups.

Purpose of the Study:

• To investigate the multiple ionization and subsequent fragmentation of nitromethane in the near-infrared (near-IR) region.
• To elucidate the mechanisms, such as rescattering, driving the dissociation of nitromethane ions.
• To identify and characterize different nitromethane isomers and their dissociation pathways.

Main Methods:

• Experiments utilizing linearly and circularly polarized laser fields.
• Employing an asymmetric few-femtosecond (fs) laser field with two colors (ω/2ω).
• Analysis of kinetic energies of ionic fragments and mass spectrometry to identify dissociation channels and isomers.

Main Results:

• Multiple ionization leading to dication and trication formation was observed, primarily driven by electron rescattering.
• Direct cleavage of the C-N bond was identified as a dominant fragmentation channel.
• The study confirmed the existence of at least three nitromethane isomers and characterized their dissociation behavior, including an asymmetric charge distribution channel in the dication dependent on laser intensity.

Conclusions:

• The rescattering process is the main mechanism for generating fragmenting nitromethane dications and trications.
• The ω/2ω fs asymmetric field enables accurate identification of dissociation channels and provides insights into electron correlation effects.
• Higher laser intensities reveal contributions from deeper electronic orbitals (HOMO-1) in double ionization, significantly altering fragmentation patterns.