  We have established a well-defined dome shape Tc curve in Ir0.94-xRhxSe2
superconductors. The maximum Tconset of 9.6K was obtained at x=0.36, at which
the Se-Se separation in the dimer anion is the longest. Simultaneously, the
destabilization of Se-Se dimers accompanied by partial elec-tron-transfer from
the Ir/Rh to the chalcogenide ions result-ed in the emergence of optimal Tc.
