Unimolecular dissociations of excited C3H6O+: A photoelectron—photoion coincidence study of cyclopropanol and allyl alcohol

The photoelectron spectrum of cyclopropanol has been determined and the first few bands have been assigned to the respective ionization processes. The dissociative photoionization of cyclopropanol and allyl alcohol has been studied by means of HeIα photoelectron—photoion coincidence spectroscopy. The breakdown diagrams of the two corresponding radical cations are practically indistinguishable within the entire energy range investigated (= 5 eV). This implies that extensive isomerizations to a single or to a mixture of common precursor structure(s) precede the dissociative processes. The currently available information on the structure of this reactant and, in particular, the role of other C₃H₆O⁺ isomers is discussed. The kinetic and thermodynamic aspects of the present results are outlined. Although three generations of daughter ions are involved, the relative importance of the different fragmentation pathways could be determined. The RRKM analysis of the coincidence data suggests that the formation of the ethylene cation by loss of a CO molecule from the parent ion hardly competes with the other four primary fragmentation reactions in the sense of the statistical theory of unimolecular reactions.