A comparative theoretical analysis of the photochemistry of the methyl radical and related systems

Portions of the ground and 3s,3px,y,z Rydberg excited state C–H and C–H2 fragmentation pathways are computed for the CH3 radical at the 4-31G+Rydberg+CI level. It is concluded that the B̃ state photochemistry of CH3 should give principally C–H bond rupture in analogy with the N–H bond rupture occurring in the à state of NH3. Higher energy photolyses should give a mixture of products whose mechanisms of formation will be difficult to establish. Rydberg extended molecular orbital and state correlation diagrams are developed for these transformations. The theoretical relationship between the behavior of the B̃ state C–H bond rupture surface in CH3 and the fragmentation occurring in the à states of NH3, H2O, and CH4 is established. Finally, an analysis is made as to the probable adiabatic photochemistry of the 3s Rydberg states of alkyl radicals.