Highly inverted vibrational level populations are found for ClO fragments resulting from the UV photodissociation of OClO((2)A(2) nu (1) > 20) into ClO(X (2)Pi (Omega),upsilon ,J) and O(P-3(J)) fragments. These distributions depend significantly on the spin-orbit J state of the oxygen O(P-3(J)) partner atom. In contrast, the ClO rotational excitation is modest. Distinct rotational structure is visible in the O (P-3(J)) photofragment yield spectrum recorded from the highly excited OClO ((2)A(2) nu (1) = 21) vibronic band, which is indicative for hitherto unforeseen long dissociation lifetimes of very highly excited OClO. The data point towards an unexpected nearly-linear and highly asymmetric dissociation geometry. Carrying out near-threshold fragmentation experiments of OClO ((2)A(2)0,0,0)--> ClO (X (2)Pi (3/2) upsilon = 0, J) + O(P-3(2,1,0)) the dissociation energy D-0 of OClO has been accurately determined to 247.3 +/-0.5 kJ/mol.