To make the diabatization of these quantities possible we are going to assume that the electronic ground state remains unaffected by molecular vibrations, i.e. |ψ FC GS ⟩ = |ψ dist GS ⟩. This is a reasonable assumption if the ground state has a closed shell configuration and is energetically well separated from the excited states which precludes any mutual mixing. The magnitude of the transition dipole moment (|⃗ µ GS→α | 2 ) cannot be converted directly into the new basis. First, the individual Cartesian components have to be calculated in the new basis. For example, the x-component is calculated as: