A method is demonstrated for the determination of intermolecular energy transfer efficiencies in systems chemically activated by nuclear recoil reaction. Relative vibrational energy transfer efficiencies are determined for highly excited cyclobutane-t formed with ∼5 eV of internal energy in the hot tritium for hydrogen replacement reaction on cyclobutane in the presence of several inert bath gases. The pressure dependence of the hot yields is used to probe the overall reaction mechanism and results indicate that a sizable fraction of the hot reaction product does not undergo competitive unimolecular decomposition. The general systematics of these side reactions are discussed. From the composition dependence of the unimolecular reaction at a constant pressure of 800 torr, the relative energy transfer efficiencies for the respective bath gases are found to be C-C4H8, 1.0; CF 4, 1.05; N2, 0.32; He, 0.12; Ne, 0.24; Ar, 0.25; Kr, 0.31; Xe, 0.39. Simple collision models for the cyclobutane-noble gas cases suggest V-T transfer occurs most efficiently through delocalized interactions. Furthermore, angular momentum considerations indicate low impact parameter collisions are most effective in forming transition modes through which statistical redistribution of energy can occur. Copyright © 1977 American Institute of Physics.