Observing elusive tetroxides in gas-phase radical reactions supports the Russell mechanism

Organic peroxy radicals (RO₂) are important intermediates for oxidation processes in aerobic chemical systems. Their self- and "cross"-reactions (i.e., with themselves and other RO₂) are increasingly receiving attention in a wide range of applications, from atmospheric chemistry to cancer therapies. However, their mechanism has been debated for decades. The Russell mechanism, widely assumed for these reactions today, is characterized by a tetroxide intermediate, only observed once and partially since its postulate in 1957. Here we report the observation of tetroxides in the gas-phase reactions of different RO₂ by direct mass spectrometry, in which ionic and gas-phase dimerization could be ruled out. Within the uncertainties in the kinetic profiles, the lifetime for CH₃OOOOCH₃ was determined to be in the range 0.2 and 200 milliseconds, consistent with an intermediate and supporting the Russell mechanism.