The bubble build-up following Rydberg state excitation in rare gas matrixes was modeled on a system comprising NO mols. trapped in Ar matrixes. The bubble formation was probed in real time using the time-resolved fluorescence depletion technique. The NO mols. were excited to their A2S+/3ss(v=0) state. Following excitation, the cage reached its equil. configuration on a timescale of 3.8-4.5 ps, depending on the excitation energy. [on SciFinder (R)]