Theoretical investigations on the vibronic coupling effect and NBO Studies of Stability on the GeX2 (X=F, Cl, and Br) molecules

The contemporary paper refers back to the instability of linear in GeX2 (X=F, Cl & Br) molecules because of the vibronic coupling effect. Optimization and the following frequency calculations in those molecules found out that every one of those molecules were unstable in high symmetry linear (with D∞h symmetry) geometry and their systems have been bent to lower C2v symmetry geometry. On this work, we've used, TD-DFT (B3LYP/6-31G (d) calculations to gain the strength curves of the ground and excited in the bending directions Q (u) of compounds 1−3. The vibronic coupling interaction between 1g+ ground and the first 1u excited states in the Q (u) direction via (1g+ + 1u) ⊗ u PJTE problem was the reason for the symmetry breaking phenomenon. Additionally, changing atoms with different elements together with the electronegative exchange and the degree of overlap at once have an effect on the pattern of molecular orbitals. The NBO calculations were carried out to define a stability measure through the stabilization energy, E2 parameter. According to the consequences received from the vibronic principle of PJT, the bent shape of those analogs is the result of LP(3) X → LP*(2)Ge1 electron delocalization .The PJT stabilization strength decreases from compound 1 to compound three. Moreover, by the decrease of the energy gaps between reference states (Δ) the primary force constant of the ground state in the Q (u) direction (K0) could decrease from compound 1 to compound 3.