Finally, Figure compares our spectrum to an earlier accurate simulation by Tarroni and Carter . This earlier work used internally contracted multi reference configuration interaction method in a large basis set (cc-pV5Z) to thoroughly scan the vicinity of the minima on both potentials. Similarly to our work, Tarroni and Carter did not account for the potential at distances reaching the dissociation limit. In their work, Tarroni and Carter used a diabatization method based on the adiabatic energies and configuration interaction coefficients, which avoids calculation of the non adiabatic couplings.