Trigonal pyramidal molecules orbital interactions

In the case of H3O+, the molecule is a trigonal pyramid like isoelectronic NH3. The reason is that the interaction between 02p and His orbitals is greater if the molecule is nonplanar. The bonding energy to 02s is not greatly diminished by pyramidalization. In this case, as well as in the case of H2O and OH , one MO is similar to 2s and the three other occupied MOs are similar to 02p. Unoccupied MOs are high in energy. 

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