H D EXCHANGE-REACTION AT GRAPHITIC CH GROUPS BY THERMAL H(D) ATOMS/

Ultrathin C:H films were produced by hydrocarbon ion-beam deposition a t Pt(100) single crystal surfaces covered with a monolayer of graphite . Temperature and thermal H(D) impact induced effects were studied wit h HREELS and AES. C:H film surfaces which exhibit only aromatic sp(2) CH groups, HC=CH, get deuterated at a temperature independent rate wit h an apparent cross section of about 1.3 Angstrom(2). After sufficient D exposure at 350 K eventually only sp(3) CHD groups cover the surfac e as deduced from the C-H(D) stretch mode structure in HREEL spectra. At 600 K the radicalic intermediate surface HDC-CH groups generated by D addition to sp(2) groups can split off H or D through thermal activ ation, thereby transforming the group back to sp(2). Thereafter in HRE EL spectra both, sp(2) and sp(3) contributions were measured in the C- H(D) stretch frequency regions. Due to a kinetic isotope effect the su rface H is preferentially removed by this reaction. C:H film surfaces under impact of H atoms erode chemically via thermally activated relea se of hydrocarbon species. As expected, an isotope effect was also obs erved in the erosion reaction proceeding from the radicalic intermedia te.