Does a dissociating molecule sample the available phase space?

We argue that dissociating molecules of realistic size will not be a representative sample of the (quasi)bound phase space, particularly so for optical excitation. Analytical considerations and numerical results are presented. Attention is drawn to the faster sampling of phase space by quasibound molecules due to coupling via the continuum. It is shown that on the time scale of bond breaking a moderate amount of mixing in the initially prepared state suffices to ensure a more representative sampling of phase space. The familiar RRKM theory of unimolecular dissociation can therefore remain valid for a non very state selective initial activation.