Determine the true nature of the coupling and the ad hoc B-state used in Di-DIM diabatization for Ar2*

Determine the true nature and parametrization of the coupling between the diabatic 3p4s ^{1,3}Σ_g state and higher-lying Σ states in the argon excimer Ar2*, including a physically grounded specification of the additional adiabatic B-state and its diabatic counterpart required by the Di-DIM diabatization, instead of relying on an ad hoc potential energy curve tuned by trimer isomer comparisons.

Background

The Di-DIM approach introduced here augments the standard DIM framework with a diabatization meant to resolve a strong avoided crossing between 3p4s and 3p4p Σ states in Ar2*. To achieve this, the authors introduce an additional high-lying ad hoc adiabatic state (the B-state) to emulate the missing coupling and reconstruct a diabatic representation via a two-state rotation.

However, the authors explicitly state that the true nature of this coupling and the corresponding B-state potential energy curve are not known; consequently, they calibrate the ad hoc state by matching the lowest-energy trimer isomer while varying the depth of the B-state. Establishing the actual coupling and state character would remove the need for this heuristic and provide a principled Di-DIM parametrization.