We present transients obtained by femtosecond time-resolved spectroscopy on I-2 encapsulated in well-defined cages of the crystalline microporous SiO2 modification deca-dodecasil 3R. After pump excitation into the electronic B-state, collision-induced predissociation is observed followed by recombination into A/A' and X states, where the molecules undergo vibrational relaxation. To explain the complex time-behavior of the transient signals, molecular dynamics simulations are performed which account for the nonadiabatic transitions in I-2 and the adsorbate-framework interactions. The theoretical study shows that the total signal contains contributions from four optical transitions which are influenced by predissociation and vibrational relaxation processes. A pronounced dependence of the transient signals on the probe-laser wavelength is determined by the position of the resonance window for the optical transition.