  Enviroment - caused dissipation disrupts the hamiltonian evolution of all
quantum systems not fully isolated from any bath. We propose and examine a
feedback-control scheme to eliminate such dissipation, by tracking the free
hamiltonian evolution. We determine a driving-field that maximizes the
projection of the actual molecular system onto the freely propagated one. The
evolution of a model two level system in a dephasing bath is followed, and the
driving field that overcomes the decoherence is calculated. An implementation
of the scheme in the laboratory using feedback control is suggested.
