Interactions of CHCl3 molecules with a crystalline ice grown on Pt(111) studied by metastable impact electron spectroscopy

Electron emission spectra obtained by thermal collisions of He*(2(3)S) metastable atoms with chloroform (CHCl3) molecules adsorbed on a crystalline ice grown on Pt(111) were measured together with the photoemission spectra, to probe the chemical processes occurring at the outermost ice layer. Our data show that the CHCl3 molecules are adsorbed on the topmost ice layer with their H atoms towards the substrate at 35 K, mainly through weak electrostatic interactions. Further, upon heating of the substrate just below the desorption temperature (120 K), the molecules are found to migrate from the topmost layer to the inner layers owing to thermal fluctuation, contrary to a simple physisorption model proposed so far. (C) 2003 Elsevier Science B.V. All rights reserved.