Dissociative charge exchange of CH5+ with Cs, coupled with quasiclassical trajectory calculations on an ab initio PES for CH5, has been used to probe the structure of the CH5+ cation. Product kinetic energy release distributions and branching ratios for CH5 -> CH4 + H and CH5 -> CH3 + H-2 have been compared. The agreement of the product branching ratios provides evidence for the fluxional nature of CH5+.