Fragmentation of doubly charged argon clusters is reported. Neutral ar
gon clusters are excited with monochromatized synchrotron radiation in
the energy regime of the argon L3/L2 absorption edges (240-260 eV) le
ading predominantly to cluster dication formation. All charged particl
es are detected in a photoelectron-photoion-photoion-concidence (PEPIP
ICO) experiment. Symmetric and asymmetric charge separation reactions
(Coluomb explosion) are identified for clusters below the critical siz
e of stable dication formation. The peak shapes of the coincidence sig
nals are investigated as a function of neutral cluster size. Character
istic changes in peak shape are observed which are used to derive frag
mentation mechanisms involving sequential evaporation of neutrals befo
re and after charge separation. The spectra indicate in accordance wit
h low kinetic energy releases occurring in charge separation of large
dissociative cluster dications (Arn2+, with n > 50) that due to large
charge separation distances the momenta of both singly charged fragmen
ts are not any more directed into opposite direction, as it is typical
for Coulomb explosion. The results are compared to collision induced
fragmentation of mass selected argon cluster dications as well as phot
on stimulated desorption spectra of condensed argon.