VUV PHOTOCHEMISTRY OF ORIENTED MOLECULES - METHYLCHLORIDE ON HIGHLY ORIENTED PYROLYTIC-GRAPHITE

The photoionization of CH3Cl adsorbed on highly oriented pyrolytic gra phite has been investigated as a function of the photon energy in the range 13-35 eV. Two ions were detected -CH3+ and H+ - which show diffe rences in their coverage and energy dependences. At very low coverages only H+ ions are produced, while at higher coverages (still in the mo nolayer regime) CH3+ ions are also observed, reflecting a change in th e orientation of the molecule on the surface as a function of coverage . The cross-section curves as a function of the photon energy for both ions show a maximum at 22 eV, while the onsets are at 16 eV for CH3and 19 eV for H+. (C) 1997 Elsevier Science B.V.