CORRELATED-PAIR FRAGMENTATION AND CHARGE-TRANSFER OF CO2 CLUSTERS FROM ATOM-SPECIFIC 1S CORE LEVEL EXCITATION

Correlated pair fragmentation processes, for C 1 s core level excitation of free CO2 molecules and CO2 clusters, have been investigated by "Zero Kinetic Energy" (ZEKE) electron spectroscopy and a (triple) ZEKE electron-ion-ion coincidence technique. For free CO2, the main fragmentation channels observed are the coffelated ion pairs C+/O+, O+/O+, O+/CO+. These correlated pairs of cations originate from fragmentation of a CO2 dication which is formed by Auger-type relaxation of the primary 1 s-1 core hole state. Surprisingly, for CO2 clusters this fragmentation channel is quenched, and correlated pair formation between intact cluster ions, i.e. CO2+/CO2+, CO2+/(CO2)2+ and (CO2)2+/(CO2)2+, become the dominant channels. This observation is explained by a fast Charge transfer within the cluster, leading to redistribution of the two positive charges. For excitation to the CO22pi(u)(pi*) resonance, a possible mechanism for this intra-cluster charge transfer is the participator valence Auger process following Auger core hole relaxation.