ON THE OUTCOME OF THE REACTIONS BETWEEN HYDROCARBON RADICALS AND O$_{2}$ IN HELIUM NANODROPLETS
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Date
2012
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Ohio State University
Abstract
Helium nanodroplet isolation and infrared laser spectroscopy are used to investigate the CH$_{3}$ + O$_{2}$ and C$_{3}$H$_{3}$ (propargyl) + O$_{2}$ reactions. The hydrocarbon radicals are generated in an effusive pyrolysis source located upstream from a differentially pumped O$_{2}$ gas pick-up cell. In this experimental configuration, the reaction occurs between sequentially picked-up and presumably cold fragments. The CH$_{3}$ + O$_{2}$ reaction leads barrierlessly to the methyl-peroxy radical, and despite having to dissipate an energy of approximately 30 kcal/mol, the infrared spectra reveal a large abundance of droplets containing the cold CH$_{3}$O$_{2}$ radical. Theoretical studies have predicted an approximately 2-4 kcal/mol barrier in the entrance channel of the C$_{3}$H$_{3}$ + O$_{2}$ reaction. Therefore, we initially expected to see a weakly bound "entrance channel" C$_{3}$H$_{3}$--O$_{2}$ van-der-Waals complex, given the rapid cooling provided by the dissipative helium environment. However, only the trans-acetylenic isomer of the propargyl-peroxy radical is observed. The dipole moment of this species is measured with infrared laser Stark spectroscopy.
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Author Institution: Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556