HDexchange reaction at graphitic CH groups by thermal H(D) atoms

Ultrathin C:H films were produced by hydrocarbon ion-beam deposition at Pt(100) single crystal surfaces covered with a monolayer of graphite. Temperature and thermal H(D) impact induced effects were studied with HREELS and AES. C:H film surfaces which exhibit only aromatic sp2CH groups, HCCH, get deuterated at a temperature independent rate with an apparent cross section of about 1.3 Å2. After sufficient D exposure at 350 K eventually only sp3CHD groups cover the surface 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 sp2groups can split off H or D through thermal activation, thereby transforming the group back to sp2. Thereafter in HREEL spectra both, sp2and sp3contributions were measured in the CH(D) stretch frequency regions. Due to a kinetic isotope effect the surface H is preferentially removed by this reaction. C:H film surfaces under impact of H atoms erode chemically via thermally activated release of hydrocarbon species. As expected, an isotope effect was also observed in the erosion reaction proceeding from the radicalic intermediate.