Photoionization of Isomers. Unimolecular and Bimolecular Reactions of the Ions.

1-Butene, -2-butene, isobutene and methylcyclopropane have been photoionized with the resonance lines of krypton (10.0-10.6 eV) and argon (11.6-11.8 eV). We have determined that the internally excited ion and, to a much lesser extent, the ion isomerizes to the structure. In both cases the extent of isomerization increases, approximately by a factor of ten when the photon energy is increased from 10 to 11.7 eV. An inert gas, neon, quenches the isomerization of the ion and, to a much lesser rextent, that of the ion. The unimolecular fragmentation of the isomeric ions has been examined at 11.61-11.8 eV. In this energy range the dissociative lifetime of was found to be at least 5 × 10 s, and collisional quenching of the dissociative process is already noticeable at pressures in the 10 torr range. The rate coefficients for the reaction occurring in the isomeric CH systems have been determined under conditions where the structure of the reacting ion is established. The values in cm/molecule · second are 1-CH - 6.0 ± 0.5 × 10, -2-CH - 0.37 ± 0.1 × 10, -CH - 5.4 ± 0.4 × 10. At pressure below 10 torr, the internally excited produced in the reaction dissociates along various channels with relative probabilities depending upon the structure of both the ionic and neutral reactant. Above 10 torr collisional quenching of is noted.