Femtosecond laser pulse excited NaI molecules interacting with infrared control fields are studied. Adapting these to be in- or out-of-phase with the vibrational motion results in an effective heating or cooling of the system. It is shown that this allows to influence the predissociation dynamics and also, to control the branching ratio between ground state predissociation and excited state dissociation. The results are discussed within the Landau-Zener theory, taking the wave-packet motion and the field shifted potential curves into account. (c) 2005 Elsevier B.V. All rights reserved.