Metastable ion studies. IV—thermochemistry and ion structures among fragmenting [C3H6]+· ions

Abstract Metastable ion peak shapes, dimensions and relative abundances have been measured for the three fragmentations [C 3 H 6 ] + · → [C 3 H 4 ] + · + H 2 , [C 3 H 6 ] + · → [C 3 H 5 ] + + H· and [C 3 H 6 ] + · → [C 3 H 3 ] + + H 2 + H·. [C 3 H 6 ] + · ions were derived from propene, cyclopropane, tetrahydrofuran, cyclohexanone, 2‐methyl but‐1‐ene and cis ‐pent‐2‐ene. Activation energies for these fragmentations have been evaluated. Three daughter ion dissociations ([C 3 H 5 ] + → [C 3 H 3 ] + + H 2 , [C 3 H 5 ] + → [C 3 H 4 ] + · + H· and [C 3 H 4 ] + · → [C 3 H 3 ] + + H·) have been similarly examined. Ion structures have been determined and the metastable energy releases have been correlated with the thermochemical data. It is concluded that the molecular ions of propene and cyclopropane become structurally indistinguishable prior to fragmentation and that differences in their metastable ion characteristics can be ascribed wholly to internal energy differences; the latter can be correlated with the photoelectron spectra of the isomers. The pathway for the consecutive fragmentation which generates the metastable ion peak ( m/e 42 → m/e .39) has been shown to be equation image It is likewise concluded that fragmentating [C 3 H 6 ] + · ions generated from the various precursor molecules are also structurally indistinguishable and cannot be classified with either molecular ion of the isomeric C 3 H 6 hydrocarbons.