The optical dissociation of I-2 can be markedly suppressed, if the I-2 molecule is weakly bound to one or more rare-gas (Rg) atoms (cage effect). A classical simulation of this process gives a fast disappearance of the cage effect and of the fluorescence intensity, as soon as the optical excitation energy E(omega) exceeds the dissociation energy of I-2 by a certain amount of energy, which is controlled by the binding energy of I-Rg(n) in the ground state. For lower E(omega) the van der Waals potential between I-2 and Rg(n) is strong enough in the asymptotic region to prevent the separating iodine atoms from dissociating. The oscillating I atoms can then transfer part of their vibrational energy to the Rg motion till the rare-gas atoms are evaporated. This mechanism gives a fluorescence spectrum of I-2 with a cutoff at higher vibrational energies-smeared out only by the thermal excitation of the ground-state complex. The dependence of the spectrum on temperature and potential parameters has been investigated. At high excitation energies E(omega) a spectrum with an isolated peak can occur, if the van der Waals binding energy is increased or if more than one rare-gas atom is bound to I-2. Other mechanisms which could result in a cage effect at higher E(omega) require a hard collision between an I and a rare-gas atom immediately after excitation. This is possible at high temperatures or for a linear conformation I-I-Rg. For an extended range of photon energies the simulations gave high yields of I-Rg(n) fragments from a I-2-Rg(n) beam.