Abstract Measuring the G values of ketyl radicals, benzophenone has been used as a probe to study the energy transfer mechanism in trioctylphosphineoxide(TOPO)–cyclohexane(CH) and tributylphosphate(TBP)–CH systems under pulse radiolysis. Results showed that there was a process of energy transfer between the excited CH and TBP or TOPO, which coincided with our previous experiments on final product analysis. Rate constants (k) of energy transfer and GCH∗ (G value of singlet cyclohexane), which are k=4.8×109 dm3 mol−1. S−1, GCH∗=1.3×0.1 for TBP and k=8.3×1012 dm3 mol−1 s−1, GCH∗=1.4±0.1 for TOPO, were obtained by Stern–Volmer method. The abnormality of the rate constant for TOPO is discussed. Another process fitted with WAS equation was assumed to be geminate ions scavenging, and the α=7.3, Ggi=3.8±0.1 for TBP, α=649, Ggi=3.7±0.1 for TOPO, were gained. Meanwhile the mechanism of the latter process were also discussed.