The spin-orbit coupling was calculated at the hopping point for each instanton as well as at the MECP. It was computed using multi-configuration quasi-degenerate perturbation theory (MCQDPT), the multi-state analogue of MRMP, along with a full Breit-Pauli Hamiltonian. Since GAMESS currently only allows a single set of orbitals as input for MC-QPDT calculations of the SOC, we generated a common set of state-averaged orbitals based on the separate sets of singlet and triplet orbitals used for the state-specific calculations.