Density functional theory DFT (PBE0) with basis set aug-cc-pV(Q+d)Z has been used to compute molecular structures, electric dipole moments and hardnesses of ground and selected electronic excited states of sulfur trioxide. Vertical excitation energy and oscillator strength are given for each state at the same level of theory. With the use of the time-dependent TD-B3LYP/aug-cc-pVQZ approach, static linear and nonlinear optical (NLO) properties were studied. Ground state properties, excited states, and transition states were modeled using DFT/PBE0, CIS and CIS(D) and QST2 and QST3 respectively. Geometrical and electrical properties of ground and excited states have been presented. Four local minima structures of SO3 were distinguished in addition to SO3 (D3h) global minimum where the CS symmetry square one is the least stable. CIS and CIS(D) calculations revealed insignificant variations in geometrical parameters among triplet and singlet excited states of the global minimum. It is observed that the state of minimum polarizability and hyperpolarizabilities is associated with the geometry of minimum energy content. The impact of symmetric stretching frequency on the mean dipole polarizability <α> and anisotropy Δα of the global minimum isomer have been fitted to a fourth order Taylor series expansion. Our calculated values of for n = 1,2 are and while those of are and respectively.
Sulfur trioxide, Hyper, Polarizabilitiy, NLO, TD, DFT, CIS