Geometries and energies of the excited states of O3 from a b i n i t i o potential energy surfaces

Abstract

The geometries and relative energies of the nine lowest states of the ozone molecule have been determined in C_2v symmetry from ab initio configuration interaction calculations in a [3s2p1d] contracted Gaussian basis. Calculations were carried out over a two‐dimensional grid of points in C_2v symmetry to locate the optimum geometrical parameters R and ϑ for each state. For the ground ¹A₁ state the calculated properties (with experimental values in parentheses) are as follows: R_e=1.299 Å (1.271 Å), ϑ_e=116.0° (116.8°), ω₁=1235 cm⁻¹ (1110 cm⁻¹) and ω₂=707 cm⁻¹ (705 cm⁻¹). Of the excited states only the lowest ³B₂ state is found to have an adiabatic excitation energy (0.92 eV) less than the dissociation energy (D_e=1.13 eV) and hence to be a likely bound species. The ¹B₂ state responsible for the strong absorption in the Hartley band (4.7–5.8 eV) is stabilized by asymmetric distortions away from its equilibrium C_2v geometry (R_e=1.405 Å, ϑ_e=108°) suggesting unequal bond lengths for this state or else purely dissociative behavior. The ring (2¹A₁) state (R_e=1.449 Å, ϑ_e=60°) is found to lie 1.20 eV above the ground state, while the remaining five states have adiabatic excitation energies ranging from 1.4 to 3.6 eV. The implications for photodissociation of O₃ are discussed.