A complete characterization, based on fs pump-probe spectroscopy and mol. dynamics simulations, is presented of the ultrafast dynamics of electronic bubble formation in solid para-H2 upon impulsive excitation of impurity-doped sites, which correlate with the lowest Rydberg state of the NO impurity. The high temporal resoln. of the expt. allows one to identify three time scales in the structural dynamics. A 1st ultrafast expansion (<150 fs), assocd. with the release of .apprx.80% of the excess energy available to the system after excitation, is accompanied by a transient narrowing of the spatial distribution of the 1st shell of H2 mols. around the impurity. In a subsequent stage (up to .apprx.800 fs), the cavity expansion slows down, and energy starts to flow irreversibly into the crystal. Finally, the lattice undergoes a slow structural reorganization at the impurity site (5-10 ps). A weak low-frequency recurrence, probably assocd. with an elastic response of the crystal, is obsd. at .apprx.10 ps. The absence of polarization dependence indicates that the dynamics is largely dominated by translational (radial) motions of the mols. surrounding NO and not by the rotational motion of the impurity. Mol. dynamics simulations with temp. corrections, to mimic zero-point fluctuations, fully support the exptl. results and show that the bubble model is suited to describe the dynamics of the system. Apparently the response of the medium around the impurity at short times is typical of a liq. solvent rather than that of a solid. [on SciFinder (R)]