Next, we recast the formalism to treat it any low-dimensional potential that vanishes or may be assumed to vanish when the subsystems separate, i.e., the LD potential need not be the sum of the potential of X and the potential of Y, and the AD potential need not be the interaction between two subsystems. We let 𝐑 A2 denote any geometry where the system is dissociated or where the AD potential is to be approximated as zero. We employ a diabatic representation in which