Coulomb explosion of an Na-12 cluster in a diabatic electron-ion dynamicalpicture

We present non-adiabatic simulations of the excitation and de-excitation of an Na-12 sodium cluster irradiated by intense femtosecond lasers. Both ele ctronic and ionic degrees of freedom are explicitly accounted for, whatever nonlinear regime is accessed. We find that the Coulomb fragmentation of th e thus excited cluster depends sensitively on the laser frequency. We furth ermore show that in the first 100 fs following the laser excitation, ionic degrees of freedom can safely be considered to be frozen. They then couple quickly to the electronic ones, within about another 100 fs, well before el ectronic excitation has fully levelled off.