Infrared Laser Spectroscopy of the CH<sub>3</sub>OO Radical Formed from the Reaction of CH<sub>3</sub> and O<sub>2</sub> within a Helium Nanodroplet

Helium nanodroplet isolation and infrared laser spectroscopy are used to investigate the CH<sub>3</sub> + O<sub>2</sub> reaction. Helium nanodroplets are doped with methyl radicals that are generated in an effusive pyrolysis source. Downstream from the introduction of CH<sub>3</sub>, the droplets are doped with O<sub>2</sub> from a gas pick-up cell. The CH<sub>3</sub> + O<sub>2</sub> reaction therefore occurs between sequentially picked-up and presumably cold CH<sub>3</sub> and O<sub>2</sub> reactants. The reaction is known to lead barrierlessly to the methyl peroxy radical, CH<sub>3</sub>OO. The ∼30 kcal/mol bond energy is dissipated by helium atom evaporation, and the infrared spectrum in the CH stretch region reveals a large abundance of droplets containing the cold, helium solvated CH<sub>3</sub>OO radical. The CH<sub>3</sub>OO infrared spectrum is assigned on the basis of comparisons to high-level ab initio calculations and to the gas phase band origins and rotational constants.