Decompositions of Ionized Isopropyl Methyl Ether: Complex-Mediated and Direct Processes in Unimolecular Dissociations

Article abstract of DOI:10.1021/j100317a030

Methane and methyl losses from ionized isopropyl methyl ether (1) were characterized to improve our understanding of ion-neutral-complex-mediated dissociations in the gas phase.Photoionization appearance energies demonstrate that the onsets for the two reactions differ by only 2+/-1 kJ mol^-1, consistent with the two processes being related by a common bond cleavage.Isotope effects confirm that the transition states for bond scission to form the complex and subsequent hydrogen transfer to form methane are at very similar energies.Loss of methane becomes insignificant 20-30 kJ mol^-1 above its onset, whereas loss of methyl increases rapidly for at least 100 kJ mol^-1 above threshold.From this it is concluded that the decompositions of 1 are complex-mediated near threshold but shift to a direct mechanism at higher energies, i. e., that decomposition is ion-neutral-complex-mediated over only a narrow range of energies just above threshold.