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 characterized with vibrational (HREELS) and thermal desorption (TDS) spectroscopies. Four reaction steps could be identified to proceed in the layers exposed to D. In a fast step D atoms add to the aromatic ring stepwise 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 methylene group is saturated by D addition. A third slow step is H abstraction from the cyclohexane ring with subsequent D addition. In a fourth slow step the remaining I-I atoms in the methyl groups get exchanged by D towards fully deuterated dimethyl-cyclohexane as the final product. The reactions observed resemble striking similarities with the respective reactions in an organic chemistry environment.