The highest occupied molecular orbital (HOMO)of difluoromethane (CH,F,) has been firstly studied by binary (e, 2e) electron momentum spectroscopy (EMS), at the impact energy of 1200 eV plus binding energy, and using symmetric non-coplanar kinematics. The experimental momentum profile of the HOMO is compared with Hartree-Fock (HF)and density functional theory (DFT) methods with various basis sets. The experimental measurement is well described by the HF and DFT calculations except for the low-momentum region. (C) 2004 Elsevier B.V. All rights reserved.