The binding energy spectra of CF3I in the energy range 9-15 eV have been measured by a newly developed high resolution (e, 2e) spectrometer with 0.5 eV energy resolution. The two spin-orbit splitting components 5e(3/2) and 5e(1/2) of iodine lone-pair orbital have been partially resolved and their individual electron momentum distributions have been obtained, together with their branching ratio as a function of momentum. The experimental results show the obvious relativistic effects on the wavefunctions for 5e(3/2) and 5e(1/2) orbitals. (C) 2008 Elsevier B.V. All rights reserved.