CH₃Cl/Cu(410): Interaction and Adsorption Geometry

Abstract

The Rochow process is the most common technology used to prepare organosilicon compounds on an industrial scale, and yet the mechanism is still not well understood. It involves the reaction of methyl chloride (CH3Cl) with silicon, catalyzed by copper. To understand the elementary steps of the reaction involved, we studied the molecular adsorption of CH3Cl/Cu(410) at 100 K and its complete desorption at higher temperatures, 100 K < TD < 200 K. Temperature-programmed desorption (TPD) spectra show two CH3Cl desorption peaks. We attribute the low temperature TPD peak (TD ≈ 120 K) to CH3Cl desorbing from both step-edges and terraces and the high temperature TPD peak (TD ≈ 160 K) to CH3Cl desorbing from the step-edges. Infrared reflection–absorption spectra (IRAS) indicate that at low CH3Cl coverage (Θ = 0.06 ML), CH3Cl adsorbs with its molecular axis (Cl–C bond) aligned either parallel or perpendicular to [001]. At high CH3Cl coverage (Θ ≥ 0.09 ML), CH3Cl adsorbs with its molecular axis aligned perpendicular to [001].