We report here the first measurements of the momentum profile of highest occupied molecular orbital and the complete valence shell binding energy spectra of 1,3-cyclohexadiene with impact energies of 600, 1200 and 2400 eV by a binary (e, 2e) spectrometer, The turn-up at low momentum could not be described by plane wave approximation calculations, but can be accounted for using the distorted wave effects. In addition, the distorted wave effects well predicted the experimental trends at lower and higher impact energy. (c) 2005 Elsevier B.V. All rights reserved.