DEUTERATION OF PHYSISORBED XYLENE WITH THERMAL D-ATOMS

p-xylene monolayers were adsorbed at monolayer graphite covered Pt(111 ) surfaces. The reactions of xylene with thermal D atoms were characte rized with vibrational (HREELS) and thermal desorption (TDS) spectrosc opies. Four reaction steps could be identified to proceed in the layer s exposed to D. In a fast step D atoms add to the aromatic ring stepwi se breaking double bonds thereby transferring the ring C atoms to sp(3 ) hybridization. In a second also fast step, H atoms in methyl groups at aromatic rings undergo an abstraction reaction to HD with a benzyl radical as an intermediate which is pi-stabilized. Subsequently, the m ethylene group is saturated by D addition. A third slow step is H abst raction from the cyclohexane ring with subsequent D addition. In a fou rth slow step the remaining I-I atoms in the methyl groups get exchang ed by D towards fully deuterated dimethyl-cyclohexane as the final pro duct. The reactions observed resemble striking similarities with the r espective reactions in an organic chemistry environment.