DIMETHYL PEROXIDE RADICAL-CATION - A NEW THEORETICAL AND EXPERIMENTALAPPROACH TO THE C2H6O-CENTER-DOT(-ENERGY SURFACE() POTENTIAL)

The structure and the unimolecular fragmentations of the metastable di methyl peroxide radical cation have been investigated by mass spectrom etric and isotopic labeling methods as well as high-level ab initio ca lculations. In line with the theoretical results, neutralization-reion ization and charge reversal experiments suggest that ionized dimethyl peroxide bears a CH3OOCH3.+ connectivity. In the cation the O-O bond d issociation energy is larger than that of the neutral counterpart; in contrast, the C-O bond strength is slightly and that of the C-H bond s ignificantly reduced upon ionization. These energetic changes upon one -electron oxidation of CH3OOCH3 are also reflected in the NR and CR ma ss spectra of CH3OOCH3.+. Further, for metastable CH3OOCH3.+ two major fragmentation pathways are observed: 1) Loss of a hydrogen atom by cl eavage of a C-H bond is associated with a skeletal reorganization, whi ch gives rise to a proton-bound formaldehyde dimer. 2) The expulsion o f a CH3O. radical leads to protonated formaldehyde in a surprisingly s pecific double hydrogen transfer involving a [CH3OH/CH2O](.+) ion/dipo le complex as central intermediate; this complex also accounts for oth er minor fragmentation channels. The structures of intermediates and t ransition states are calculated with the BECKE 3LYP density-functional method employing a 6-311++G* basis.