Energetics and mechanism of the recoil tritium replacement reaction with cyclobutane

The energetics and mechanism of recoil hot tritium atom replacement reactions with cyclobutane are explored. Kinetic analysis of the pressure dependence for the total yields of hot replacement products is used to distinguish reactive processes. Results show that cyclobutane-t can be formed both as a stable primary product and as an excited intermediate with enough energy to undergo unimolecular decomposition to ethylene-t as reported earlier. In addition a sizable yield of ethylene-t is formed independent of the competitive unimolecular stabilization-decomposition process at all pressures explored. On the basis of energy shadowing properties in recoil hot reaction systems, it is concluded that the latter ethylene-t yield does not arise from an extremely high energy contribution to the cross section for forming excited cyclobutane-t but rather from a mechanism whose primary hot atom reaction cross section is manifest over the same energy range as the other processes observed. It is suggested that this reaction channel may arise either from carbon carbon bond cleavage on hot reaction or via an unimolecular process following hot tritium for hydrogen replacement in which decomposition occurs before statistical redistribution of internal energy. (orig.)