Chlorinated ethenes at Cu(1 1 0): adsorption, dissociation and reactions of trans-1,2-dichloroethene

The adsorption and reactions of trans-1,2-dichloroethene on Cu(1 1 0) have been investigated using reflection absorption infrared spectroscopy, temperature programmed desorption and molecular beam adsorption reaction spectroscopy. These data reveal that the behaviour of the system is critically affected by temperature and can be described in terms of three main regimes: Regime I, which occurs over 85–165 K, represents molecular adsorption in the monolayer and the multilayer where the trans-1,2-dichloroethene adsorbs with its molecular plane oriented largely parallel to the metal surface; Regime II, extending over the temperature range 170–280 K, is dominated by desorption/dechlorination events which are first initiated at 171 K, then poisoned rapidly and re-initiated at the much higher temperature of 263 K, culminating in the creation of adsorbed acetylene and Cl atoms on the surface; Regime III, spanning the temperature range of 280–500 K, is governed by the behaviour of the C2H2 molecular intermediate at the surface which, if created at low temperatures, trimerises to form benzene that subsequently desorbs. However, when created at high temperature, direct desorption of C2H2 competes effectively with the trimerisation process.