Pseudo-Jahn–Teller effect in Si₄X₄ (X = F, Cl, Br, I) molecules: a theoretical investigation

ABSTRACT

The variability of planar rings in Si₄X₄ (X = F, Cl, Br, I) molecules caused by the pseudo-Jahn–Teller impact (PJTE) was evaluated as an original PJTE work. Optimisation and the following frequency calculations in these molecules illustrated that in high-symmetry planar (with D_4h symmetry) geometry, all of these compounds were unstable and their structures were puckered to lower C_2h symmetry stable geometry. Furthermore, the vibronic coupling interaction between ¹A_1g ground and the first ¹E_g excited states through (¹A_1g + ¹E_g) ⊗ e_g PJTE problem was the cause of non-planarity of the four-member ring and the symmetry breaking phenomenon in those series. The calculated gaps (Δ) between the ground state and the E_g excited state, the vibronic coupling (F) and ground state primary force constant values (k₁) were obtained from the numerical fitting of the ground state adiabatic potential energy surface with the analytical expressions of these molecules. Finally, natural bond analysis (NBO) was used for the design of the strongest interaction and natural atomic charges of these structures.

GRAPHICAL ABSTRACT

KEYWORDS:

• Tetrasilacyclobutadiene
• symmetry breaking phenomena
• pseudo-Jahn–Teller effect
• vibronic coupling constant
• natural bond analysis (NBO)