The dynamics of electron bubble formation upon excitation of the A(3ss) Rydberg orbital of NO in solid Ne was studied by femtosecond pump-probe spectroscopy. The authors observe an ultrafast expansion of the bubble, followed by a vibrational recurrence in .apprx.1.4 ps. The overall dynamics is slower than in the heavier Ar solid. Mol. dynamics simulations show that this results from the collective motion of several shells around the excited impurity, as a result of the nature of the excited NOA-Ne and the Ne-Ne potentials. Quantum effects play a negligible role in the dynamics. [on SciFinder (R)]