Extending the Shin-Metiu two electron Hamiltonian, we construct a new Hamiltonian with effective singlet-triplet couplings. The Born-Oppenheimer electronic potentials and couplings are different parameters, and the laser-free dynamics is calculated with the full. Hamiltonian and in the adiabatic limit. We compare the dynamics'. of the system using. nuclear. wave packets for different numbers of Born-Oppenheimer potentials and vibronic wave packets on a full 3-dimensional (two electron coordinates plus one nuclear coordinate) grid. Using strong fields, we show that it is possible to dynamically lock the spin state of the system by decoupling the. singlet-triplet transition via a nonresonant dynamic Stark effect in the adiabatic limit. Although a similar spin:locking, mechanism is observed in the dynamics of vibronic wave packets, multi-photon ionization cannot be neglected leading to the breakdown of the control scheme.