Site-specific fragmentation of acetone adsorbates on Si(100) in the carbon 1s absorption edge

We have investigated photon-stimulated ion desorption from acetone adsorbates on Si(100) at 93 K. The mass spectra and the excitation-energy spectra for fragment-desorption yields, along with photoabsorption spectra, were measured in the soft X-rays with energy of 270–320 eV. Methyl fragments (CH+n, n=1–3) are preferentially produced at the resonance that has been assigned to the transition of methyl carbon core level to a mixture of π∗(CH3) and 3p Rydberg. Both the desorption mass patterns and the excitation spectra for the fragment-ion yields showed a remarkable change when the samples were changed from thin layers to crystalline thick layers. The desorption mechanism is considerably changed depending on the layer thickness.