Deuterated methanol adsorption on Si(111)-(7 7) has been studied by C ls and O ls core-line synchrotron radiation photoemission and mass spectrometry of photodesorbed ions. Experiments were performed as a function of coverage and temperature. Two different C 1s photoemission peaks hint at two different adsorbed species, the first one related to the methoxy fragment produced after dissociative adsorption, the second one is attributed to a CD x species. Both peaks disappear after heating at 350°C, though the methoxy species is more reactive, and a third peak appears. The nature of the species producing the third peak was deduced by means of the mass spectra after heating the sample at 400°C and attributed to C dispersed on the silicon surface.