An experimental study via X-ray photoelectron spectroscopy at different takeoff angles of the derivatization of atomically flat, hydrogen terminated, 1 x 1 (1 0 0) Si surfaces with 1-octyne is reported. The major conclusion of the experimental analysis (that a large fraction of the grafted moieties contain unreacted pi bonds) is then compared with the results of high-level ab initio modelling with model molecules of the derivatization act. (c) 2004 Elsevier B.V. All rights reserved.