Effect of matrix electronic characteristics on trapping and degradation oforganic radical cations in solid ware gases: A case study of methylal radical cation

The matrix effects on trapping and degradation of methylal radical cation g enerated in solid argon, krypton, and xenon doped with an electron scavenge r at 16 K were investigated by EPR spectroscopy. A relatively weak characte ristic signal from trapped methylal radical cations was recorded in an argo n matrix. However, the most intense signals in this matrix result from the products of degradation of the primary cations, mainly methyl and methoxy r adicals. A comparatively low g(max) value for methoxy radical (g = 2.032) w as explained by formation of a pi-complex [CH3O.... CH2=O+CH3] upon fragmen tation of the parent cation in solid argon. In the case of a xenon matrix, the main observed species is the (CH3OCHOCH3)-C-. radical, which appears to result from proton loss in the primary cation. Both deprotonation and frag mentation products were found in krypton. The matrix effects were attribute d to the variations in ionization potentials and polarizability (or basicit y) of matrix atoms. Fragmentation predominating in argon was explained by e xcess energy resulting from highly exothermic positive hole transfer. Depro tonation in xenon is favored by basicity of the matrix atoms. Two possible mechanisms were discussed for the latter case, i.e., thermodynamic effect ( deprotonation to matrix) and kinetic effect (catalysis of intramolecular H shift by matrix atoms).