A TD- DFT Study: The Origin of Instability of Planar Structures of ClNO+ and ClNO

TD-DFT and DFT calculations were performed for ClNO and ClNO+ at B3LYP/def2-TZVPP [1] level of theory to optimized all structures. The planar forms of ClNO and ClNO+ withsymmetry were found to be a saddle point with an imaginary frequency for each. The twomolecules became stable in the form of non-planar with Cs symmetry. The stability of variousClNO forms has already been investigated [2], but no reports were found for ClNO+. In this work,Pseudo Jahn-Teller effect (PJTE) was introduced as the origin of instability of high symmetrystructures. PJTE is one of three properties of the Jahn-Teller effect. The Jahn-Teller effect isincluded three properties: the Jahn-Teller (for degenerate state), the Renner-Teller (for linearmolecules) and Pseudo Jahn-Teller (for any systems) [3]. Although high symmetry geometry ofthese molecules is linear and RT effect is expected to be effective, but the PJT effect has oftenbeen more effective on the deviation of planar structures. The main contributions of thedistortions of high symmetry (..) configurations to low symmetry (Cs) configurations were dueto mixing the σ ground state and the π excited state. The result of mixing was PJT (...)problem. The energy gap (Δ) between references states increased from ClNO+ to ClNO (0.014,1.404 eV) and the PJT stabilization energy (EPJT) unexpectedly increase. It is expected that thecontribution of vibronic coupling of the reference states decrease with increasing of the energygap. In this study because of the existence of delocalized electrons, the EPJT increase from ClNO+to ClNO[4]. The B3LYP/def2- TZVPP calculated results showed total energy differencesincreased from ClNO+ to ClNO. Generally it can be resulted that PJTE of vibronic coupling toall the excited states is just caused destabilize of the ground state in the direction nucleardisplacements (Q) [3].

Keywords:

Pseudo Jahn-Teller Effect , Vibronic Coupling , Energy Gap , Delocalized Electrons