For the matter Hamiltonian ĤM = T + V , the vibrational eigenstates |ν i ⟩ and eigenenergies E i are obtained by solving ĤM |ν i ⟩ = E i |ν i ⟩ numerically using the discrete variable representation (sinc-DVR) basis with 1001 grid points in the range of [-2.5, 2.5]. To facilitate the mechanistic studies, we diabatize the two lowest eigenstates and obtain two energetically degenerate diabatic states