Photoionization and Photodissociation of Allene Clusters in a Supersonic Molecular Beam

Abstract

The cluster photoionization mass spectrum of allene (1,2-propadiene) (C 3H4 ) has been measurd with synchrotron radiation from the electron storage ring BESSY. Cluster cations and characteristic fragmentation patterns are observed which are differing depending on the cluster size. The allene dimer decays mainly into C 3Ht and C 6Ht. The trimer fragmentation yields mainly C 7Ht, C 7Ht, and C SH9 + . These cations are formed by abstraction of methyl, ethene, and ethyl groups, respectively. The parentage of the fragmentation products has been assigned by measuring the pressure dependence of the ion signals. The energetics of the ionization and fragmentation processes has been studied by means of appearance potential measurements. From these values intermolecular binding energies of the cationic complexes are obtained. The role of stable precursor cations and the evidence of energy barriers are discussed for the dominating cluster fragmentation reactions. The role of proton transfer reactions within allene clusters is discussed in terms of charge distributions obtained from MNDO calculations.