To add further insights, CCSD(T)/Def2-TZVPP model studies were conducted in which the I + -Ph leaving group is replaced by what must be the ultimate leaving group He + , itself formed by radioactive decay of tritium. Here, unlike the C-I bond, the BDE of the C-He + bond is tiny (~1 kcal/mol) and its replacement by C2 does indeed then result in a reasonably exo-energic equilibrium (G298 -42.2 kcal/mol), augmented again by entropy gain. This serves as a reminder that C2 itself is a very high energy species.