Photodissociation Pathways of Methanol: Dissociation, Roaming, and Migration

Area of Science:

• Physical Chemistry
• Chemical Physics
• Molecular Dynamics

Background:

• Understanding molecular photodissociation dynamics is crucial for chemical reaction mechanisms.
• Deuterated methanol serves as a model system for studying complex fragmentation pathways.
• Laser-induced dissociation provides insights into excited-state molecular behavior.

Purpose of the Study:

• To investigate the two-body photodissociation pathways of deuterated methanol using single and double laser pulses.
• To identify and characterize the roaming behavior of neutral D2 fragments and their subsequent ionization.
• To elucidate the mechanistic origins of observed fragmentation channels through theoretical simulations.

Main Methods:

• Experimental measurements utilizing Infrared (IR) pump-IR probe spectroscopy.
• Coincident momentum imaging technique for fragment analysis.
• Ab initio molecular dynamics simulations: DFT for ground-state and state-averaged CASSCF for excited-state dynamics.

Main Results:

• Unambiguous observation of roaming D2 neutral behavior leading to D2+ formation.
• D2+ formation identified as a significant pathway following direct excitation to a dication.
• Two-pulse measurements indicated that migration pathways, despite low probability, are the fastest photodissociation relaxation routes.

Conclusions:

• The study confirms roaming D2 as a key dissociation channel in deuterated methanol.
• Fast migration pathways are identified as the dominant relaxation route in photodissociation.
• Combined experimental and theoretical approaches provide a comprehensive understanding of the fragmentation mechanisms.