Photodissociation dynamics of pyridine

Area of Science:

• Physical Chemistry
• Chemical Physics
• Photochemistry

Background:

• Pyridine photodissociation is crucial for understanding molecular fragmentation.
• Investigating isotopic variants (deuterated pyridine) provides insights into reaction mechanisms.

Purpose of the Study:

• To investigate the photodissociation pathways of pyridine and its deuterated analogs at 193 nm and 248 nm.
• To elucidate the role of internal conversion and electronic states in pyridine fragmentation.
• To compare experimental findings with theoretical calculations.

Main Methods:

• Multimass ion imaging techniques were employed to study the photodissociation.
• Isotopically labeled pyridines (2,6-d2-pyridine and d5-pyridine) were used to track atom exchange.
• Photofragment translational energy distributions and dissociation rates were measured.

Main Results:

• Six distinct dissociation channels were identified at 193 nm, including H atom loss and various ring-opening pathways.
• Extensive hydrogen and deuterium atom exchange was observed in 2,6-d2-pyridine prior to dissociation.
• Dissociation was found to occur on the ground electronic state following internal conversion.
• The photodissociation rate at 248 nm was too slow to measure, with an upper limit of 2x10^3 s^-1.

Conclusions:

• The study provides a detailed map of pyridine photodissociation pathways.
• Internal conversion to the ground electronic state plays a significant role in the fragmentation process.
• Experimental results were compared with ab initio calculations and Rice-Ramsperger-Kassel-Marcus theory for validation.