Photodissociation dynamics of the simplest alkyl peroxy radicals, CH 3 OO and C 2 H 5 OO, at 248 nm.

The photodissociation dynamics of the simplest alkyl peroxy radicals, methyl peroxy (CH3 OO) and ethyl peroxy (C2 H5 OO), are investigated using fast beam photofragment translational spectroscopy. A fast beam of CH3 OO- or C2 H5 OO- 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. CH3 OO exhibits repulsive O loss resulting in the formation of O(1 D) + CH3 O with high translational energy release. Minor two-body channels leading to OH + CH2 O and CH3 O + O(3 P) formation are also detected. In addition, small amounts of H + O(3 P) + CH2 O are observed and attributed to O loss followed by CH3 O dissociation. C2 H5 OO exhibits more complex dissociation dynamics, in which O loss and OH loss occur in roughly equivalent amounts with O(1 D) formed as the dominant O atom electronic state via dissociation on a repulsive surface. Minor two-body channels leading to the formation of O2 + C2 H5 and HO2 + C2 H4 are also observed and attributed to a ground state dissociation pathway following internal conversion. Additionally, C2 H5 OO dissociation yields a three-body product channel, CH3 + O(3 P) + CH2 O, for which the proposed mechanism is repulsive O loss followed by the dissociation of C2 H5 O 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(1 D) production.