Electron Momentum Distributions of the Highest Occupied Molecular Orbital of CF₃Br: Delocalization of Halogen Lone-Pair Orbitals

The highest occupied molecular orbital (HOMO) of trifluorobromomethane (CF₃Br) is studied by binary (e, 2e) electron momentum spectroscopy. The experimental momentum profile of the HOMO is compared with the Hartree-Fock (HF) and density functional theory (DFT-B3LYP) calculations. The calculated results largely depend on the size of basis sets rather than theoretical methods. Both the HF and DFT calculations using the 6-311++G** basis set give a good explanation to the experiment. Delocalization of halogen lone-pair orbitals in the series molecules CF₃X (X= F, Cl, Br) has been investigated.