We show that electronic states can be decoupled, removing the crossing between the potentials, or coupled, inducing intramolecular crossings, by applying dynamic Stark-shifts with strong nonresonant pulses. As an example, stopping and enhancing the singlet-triplet transfer between the 1(1)Sigma u and 1(3)Pi(u), excited states to create purified spin states in the Rb-2 molecule is demonstrated. (c) 2006 Elsevier B.V. All rights reserved.