We have investigated the C Is photoelectron spectra of ethylene on the Si(l 0 0)(2 x 1) surface, using high resolution photoelectron spectroscopy. The vibrational structure has been observed in the C Is spectra where the C-H stretching mode is dominant. The vibrational splittings of C Is ionized state are very similar to those in the ground state. It is found that linear coupling model is applicable in this system and this excitation process is a Frank Condon process. The curvature of potential energy surface of C-H and C-D bond is almost unchanged upon core ionization. (C) 2003 Elsevier Science B.V. All rights reserved.