In Ref. 74, the closed analytic formalism for arbitrary two-level molecular systems is presented. Without the loss of generality, such a system can be expressed in terms of the diabatic states {|0⟩, |1⟩}, which represent a broad range of chemical systems. To simplify the algebra, one assumes there is only one nuclear DOF with the coordinate R and momentum pR , and μ is always aligned along the polarization direction ê. Note that both the transition and permanent dipoles are functions of R.