Quasiclassical trajectory calculations on the CS2-CO system were performed. Analytical biexponential functions were fit to the trajectory results, and energy-dependent energy transfer transition probability functions and rate coefficients were derived. They, in turn, were used in solutions of master equations. Unimolecular rate coefficients for cyclobutane fission and cyclobutene isomerization in Ar bath gas at various temperatures were obtained. Supercollisions, collisions which transfer more than 5 times the average energy transferred in a down collision, were found to contribute to the high-energy tail of the biexponential transition probability function. To assess their contribution to the unimolecular rate coefficients, their values which were obtained from trajectory-based double-exponential transition probabilities are compared with those obtained from single-exponential weak-collision transition probabilities. For cyclobutane fission an similar to 5-fold increase in the value of the rate coefficient is found at 1000 K and similar to 7-fold increase at 1500 K when the biexponential function is used. For cyclobutene isomerization the change ranges from an similar to 7-fold increase at 500 K to an similar to 9-fold increase at 1500 K. Since the magnitude of supercollisions and, thus, the magnitude of the tail of the probability distribution can vary depending on the system, a systematic study was performed on how the high-energy tail affects the values of the unimolecular rate coefficients. It was found that for weighing factors of the strong-collision contribution to the biexponential probability function of 0.5% or 10% of that of the weak-collision contribution (with an exponential parameter of 300 cm(-1)) the rate coefficient increases with the size of the strong-collision exponent and with temperature. When the contribution of the weak-collision exponent to the energy transfer probability function was artificially removed, it was found that in some cases, 0.5% of the strong-collision part contributes similar to 70% to the overall rate coefficient while 99.5% of the weak-collision part contributes only 30%.