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

Abstract

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, CH, and acetone (83%), with minor two-body fragmentation channels leading to the formation of O + tert-butyl radical (10%) and HO + 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.

Photodissociation dynamics of the simplest alkyl peroxy radicals, CH3OO and C2H5OO, at 248 nm

“…2,4 Photodissociation experiments provide unique insights into how alkyl peroxy radicals dissociate on their excited and ground electronic states, as shown in our recent experiments on the t-butyl peroxy radical (t-BuOO). 5 Characterizing how these dynamics depend on the alkyl substituents is crucial to gaining an insight into the general reactivity of peroxy radicals and how they participate in larger chemical arenas. To this end, we investigate the photodissociation of CH 3 OO and C 2 H 5 OO at 248 nm in this work.…”

“…22 The OH fragment was found to contain very little internal energy, and thus, the authors related the experimental results to an impulsive model in which the O-O bond is cleaved repulsively. Recent work in our group considered the photodissociation of the t-BuOO radical at 248 nm, 5 for which the dominant photoproducts were O( 3 P) + CH 3 + acetone with minor contributions from two-body O 2 and HO 2 loss. The three-body dissociation products were proposed to form via repulsive cleavage of the O-O bond on the excited state, followed by rapid fragmentation of the remaining t-butoxy fragment.…”

Photodissociation of iso-propoxy (i-C3H7O) radical at 248 nm

“…This scenario has been observed in our experiment previously for three-body channels with fragments close in mass. 33,34 As such, the similarity of distributions presented in Fig. 5a and 5b is not entirely surprising.…”

Photodissociation Dynamics of the Tert-Butyl Perthiyl Radical

“…15 Recent fast radical beam studies in our laboratory investigated photodissociation dynamics of methyl, ethyl and t-butyl peroxy radicals at 248 nm. 16,17 The alkyl peroxy radicals were excited to their ̃state and coincident detection of the photofragments yielded information on the two-and three-body dissociation channels. In these species, the ̃state is repulsive along the O-O bond stretching coordinate, and its photoexcitation results in loss of O atoms on electronically excited states, leading to both two-and three-fragment dissociation channels.…”