Investigation of the two- and three-fragment photodissociation of the tert-butyl peroxy radical at 248 nm.

The photodissociation dynamics of the tert-butyl peroxy (t-BuOO) radical are studied by fast-radical-beam coincidence translational spectroscopy. The neutral t-BuOO radical is formed by photodetachment of the corresponding t-BuOO- anion at 700 nm (1.77 eV), followed by dissociation at 248 nm (5.00 eV). Photofragment mass and translational energy distributions are obtained. The major channel is found to be three-body fragmentation to form O, CH3, and acetone (83%), with minor two-body fragmentation channels leading to the formation of O2 + tert-butyl radical (10%) and HO2 + isobutene (7%). Experimental results show that the translational energy distribution for two-body dissociation peaks is close to zero translational energy, with an isotropic angular distribution of fragments. These results indicate that two-body fragmentation proceeds via internal conversion to the ground electronic state followed by statistical dissociation. For three-body dissociation, the translational energy distribution peaks closer to the maximal allowed translational energy and shows an anisotropic distribution of the plane of the dissociating fragments, implying rapid dissociation on an excited-state surface. A small shoulder in the three-body translational energy distribution suggests that some three-fragment dissociation events proceed by a different mechanism, involving internal conversion to the ground electronic state followed by sequential dissociation.