UC Berkeley

The photodissociation dynamics of the simplest alkyl peroxy radicals, methyl peroxy (CH₃OO) and ethyl peroxy (C₂H₅OO), are investigated using fast beam photofragment translational spectroscopy. A fast beam of CH₃OO^- or C₂H₅OO^- anions is photodetached to generate neutral radicals that are subsequently dissociated using 248 nm photons. The coincident detection of the photofragment positions and arrival times allows for the determination of mass, translational energy, and angular distributions for both two-body and three-body dissociation events. CH₃OO exhibits repulsive O loss resulting in the formation of O(¹D) + CH₃O with high translational energy release. Minor two-body channels leading to OH + CH₂O and CH₃O + O(³P) formation are also detected. In addition, small amounts of H + O(³P) + CH₂O are observed and attributed to O loss followed by CH₃O dissociation. C₂H₅OO exhibits more complex dissociation dynamics, in which O loss and OH loss occur in roughly equivalent amounts with O(¹D) formed as the dominant O atom electronic state via dissociation on a repulsive surface. Minor two-body channels leading to the formation of O₂ + C₂H₅ and HO₂ + C₂H₄ are also observed and attributed to a ground state dissociation pathway following internal conversion. Additionally, C₂H₅OO dissociation yields a three-body product channel, CH₃ + O(³P) + CH₂O, for which the proposed mechanism is repulsive O loss followed by the dissociation of C₂H₅O over a barrier. These results are compared to a recent study of tert-butyl peroxy (t-BuOO) in which 248 nm excitation results in three-body dissociation and ground state two-body dissociation but no O(¹D) production.