Fragmentations of hydroxymethyl radical cation: An ab initio study

The probable fragmentation channels of hydroxymethyl radical cation were studied through the H- and H-2-abstraction and C-O bond breaking reactions including their related isomerization reactions. The energy barriers for hydroxymethyl cation undergoing isomerization reactions are generally higher than those undergoing the concerted 1,2-elimination reactions to generate CHO+ and H-2. The fragmentation reaction to form CHO+ and H-2 through the 1,2-elimination pathways is the major fragmentation channel for hydroxymethyl cation, consistent with the experimental observation. H abstraction from the hydroxyl group of CH2OH+ is more difficult than that from the methylene group. The feasible path to lose H is to generate CHOH2+ through hydrogen transfer reaction as the first step and then to undergo H-elimination to generate trans-CHOW. Among all the reactions found in this study, the OH-elimination to generate CH2+ has the highest energy barrier. Our calculation results indicate that the major signals contributed from the related species of hydroxymethyl cation found in the mass spectrum should be m/e 29, m/e 30.