Electron momentum spectroscopy studies of the ethylene highest occupied 1b(3u) orbital are reported. The experiments were performed at impact energies of 400, 600 800 1000, 1200 and 1600 eV using a high resolution and high sensitivity (e, 2e) spectrometer. The orbital electron momentum distributions of 1b(3u), are presented at a wide range of impact energies, which are used to examine the validity of plane wave impulse approximation and provide an experimental analysis of distorted wave effects in the higher momenturn region of molecule with the variation of impact energy. (c) 2005 Elsevier B.V. All rights reserved.