Fragmentation of metastable methane radical ions(1+) and isotopic analogs. Kinetic energy release distributions and tunneling through a rotational barrier: experiment and theory

Abstract

The fragmentation of metastable CH/sub 4//sup +/, CD/sub 3/H/sup +/, and CD/sub 4//sup +/ ions has been studied with use of mass analyzed ion kinetic energy spectrometry (MIKES).Kinetic energy release distributions were derived from the MIKES peaks. The average kinetic energy release and metastable intensity were found to increase with ion source temperature. Appearance potential measurements indicated that the metastable reaction arises from CH/sub 4//sup +/ ions with internal energy close to the thermochemical threshold for fragmentation to give ground state CH/sub 3/(/sup 1/A/sub 1/) + H(/sup 2/S). The experimental data suggest that the origin of the metastable process is tunneling through a centrifugal barrier. A statistical model is presented and predictions of the model are compared with the experimental data.