Dissociative photoionisation of acetylene-ethane van der Waals clusters

Intracluster ion-molecule reactions have been studied by dissociative photoionization of mixed acetylene-ethane van der Waals clusters in a supersonic molecular beam. The studies were carried out by recording threshold photoelectron-photoion coincidence mass spectra of the clusters at different photon energies between 10.8 and 11.3 eV. Intracluster reactions have been observed in mixed dimer, trimer, pentamer, and hexamer clusters. In the case of the mixed dimer ion [(C2H2)(C2H6)](+) two fragment ions result from intramolecular reactions: C3H5+ (CH3 loss), and C2H4+ (C2H4 loss). This indicates that the dimer ion isomerizes into the 2-butene ion prior to dissociation, as is the case for ethylene dimer ions. Mixed trimer ions also dissociate by CH3 loss. No intracluster hydride transfer prior to dissociation is observed, although this reaction channel is important in bimolecular C2H2+ + C2H6 collisions. Two very specific intracluster reactions leading to C2H6 loss were observed for pentamer and hexamer mixed cluster ions. A model involving evaporation and intracluster reactions leading to CH3 and C2H4 loss is proposed to explain this surprising result. (Int J Mass Spectrom 199 (2000) 201-209) (C) 2000 Elsevier Science B.V.