Investigations On Processes Induced By Single-Scattering And Multiple-Scattering Of Electrons In Clusters Involving Excimer-Induced Fragmentation And A New Metastable Fragmentation Channel Observed For Arno+Asterisk Cluster Ions

A new metastable decay reaction of Ar(n)O+ cluster ions produced by the electron impact ionization of argon-oxygen clusters has been discovered, leading to the evaporation of more than two monomers in the metastable time regime. It is estimated that an energy of approx. 1 eV has to be released from the intramolecular to intermolecular modes prior to this metastable decay. In contrast to previously observed excimer-induced fragmentation of pure argon cluster ions, it has been concluded that the localized metastable state of an ionic rather than a neutral species is involved in the fragmentation. A reaction mechanism involving an electronic transition from the a2PI ArO+* (O(3P)-Ar+(2P)) excited state to the X4SIGMA- ArO+ (O+(4S)-Ar(1S)) ground state of the ArO+ complex ion within the cluster and subsequent release of considerable amount of vibrational energy to cluster modes is suggested to account for the observed fragmentation. Based on these measurements, a lifetime of approx. 2 mus is proposed for the excited state a2PI ArO+*.