Threshold photoelectron photoion coincidence study of the ethane loss from energy selected pentane ions cooled in a supersonic expansion

Abstract

The loss of C2H6 from energy selected pentane ions has been investigated by the threshold protoelectron photoion coincidence method. Breakdown diagrams are reported at room temperature and for two different conditions in a molecular beam. From the observed shift in cross-over energies the 0 K onset for the C2H6 loss is determined to be 690 ± 20 meV. This result together with information about kinetic energy release and other thermochemical data supports the earlier conclusion that the corresponding ion in the C2H6 loss is the propene ion rather than the cyclopropane ion. It is shown that rotational and vibrational energies are both active in this dissociation. The rate constants of dissociation have been measured as a function of the ion internal energy and are shown to agree with the results of Rice-Rampsperger-Kassel-Marcus calculations. Evidence is given that isomerisation of pentane to methylbutane prior to dissociation does not play an important role.