The iodine effect on the photoexcited I-(H2O)(n) relaxation pathway is studied using ab initio calculations. Critical behavior of the vertical binding energy (VBE) of the excited I-(H2O)(n) is seen at short distances between the iodine and the remaining (H2O)(n), which is correlated to the rapid experimental VEE increase within 1 ps (L. Lehr, M.T. Zanni, C. Frischkorn, R. Weinkauf, D.M, Neumark, Science 284 (1999) 635). Further comparisons of computed results with experimental data reveal that iodine detachment is a crucial step in the cluster relaxation dynamics, intrinsically different from the electron-detachment pathway of photoexcited aqueous iodide.