Triatomic Walsh diagram

Figure 9.4. Walsh diagram showing correlation of orhitals between bent and hnear triatomic molecules, and suggesting variation in orbital energy with bond angle.

Calculations on triatomic molecules, because of their theoretical and experimental significance, will be mentioned below in some detail. Herzberg s Polyatomics [6] gives diagrams of the correlation of orbitals between large and small internuclear distances in linear AH2 molecules and in linear ABa molecules [6]. Walsh, in a classic series of papers [97], gave correlations of molecular orbitals between linear and bent AH2 molecules and linear and... 

Diatomic molecules are necessarily linear, but a triatomic molecule can be either linear like CO2 and HCN or bent like SO2 and H2O. Mulliken s correlation diagram procedure was extended to tri- and tetraatomic molecules by Walsh [1], who promulgated a set of simple but remarkably viable [2, 3, 4] rules for predicting whether or not a molecule will remain linear, from the effect of the departure from linearity on the energy of its occupied molecular orbitals. 

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