Molecular orbitals for the water molecule (H2O) Molecular Orbitals for Water (H 2 O). The five occupied and the lowest three unoccupied molecular orbitals of the isolated molecule (1a 1) 2 (2a 1) 2 (1b 2) 2 (3a 1) 2 (1b 1) 2 were calculated using the Restricted Hartree-Fock wave function (RHF) using the 6-31G** basis set. b (experimental data ...