A Esmaeili - Department of Chemistry, Education,Mahallat,Iran

The structural properties of SO2 (SO2 , SO2+2, SO22+ 2, SO2- 2, SO22- 2) have been examined by means ofB3LYP/Def2-TZVPP level of theory interpretations. The results obtained showed the expected ground state structurefor compounds is linear.(D∞h symmetry) .The distortion of the high-symmetry configuration of compounds is due to thepseudo Jahn-Teller effect(PJTE), which is the only source of instability of high-symmetry configuration innondegenerate states. The negative curvatures of the ground state electronic configurations and the positive curvaturesof the excited statesof the adiabatic potential energy surfaces (APESS) which resulted from the mixing of the groundg∑+ g and excited II u states are due to the PJTE (i.e. PJTE((∑ + g + IIu) IIu problem).[1].contrary to the usualexpectation ,with the decrease of the energy gaps between reference states (Δ),the PJTE stabilization energy decreasesfrom compound 1 to compound 5.

TD-DFT, pseudo Jahn-Teller effect, imaginary frequencies,