Geometry and Electronic Structure of Carbon Trioxide

The extended Hückel form of molecular‐orbital theory, developed by Hoffmann, was used to calculate the molecular energy of CO₃ in several different assumed geometries in an attempt to find the structure of lowest energy. Energy calculations were also carried out along assumed paths of dissociation of CO₃ into CO+O₂ and CO₂+O fragments. Correlation diagrams showing how energy levels change with bond angle are given and discussed in relation to Walsh's rules for the geometry of AB₃ type molecules. Results seem to favor a planar, isosceles triangular ${\mathrm{(C}}_{\text{2υ}})$ geometry for the structure of CO₃.