Adsorption structure, energetics, and thermal reactions of vinyl chloride on Ag(111)

A study of vinyl chloride on Ag(l 1 1) by thermal desorption spectroscopy (TDS) and high resolution electron energy loss spectroscopy indicates that vinyl chloride is weakly adsorbed with the molecular plane approximately parallel to the Ag(l 1 1) surface plane. The monolayer desorbs molecularly at 119 K in a first order process with desorption activation energy of 6.7 kcal/mol and prefactor of 4.6 x 10(11) s(-1). The first few multilayers above the monolayer desorb molecularly at 92 K with an activation energy of 4.3 kcal/mol. At low vinyl chloride coverages TDS has the resolution to allow the observation that as the Ag(l 1 1) surface is heated to greater than 126 K, a small portion (<20%) of the adsorbed vinyl chloride dissociates with an estimated activation energy of 8 kcal/mol, into vinyl and Cl, which adsorb on Ag(l 1 1). Further heating to temperatures greater than 155 K results in vinyl and Cl recombination with subsequent molecular desorption in a second order process with desorption activation energy of 10.7 kcal/mol and prefactor of 2.3 x 10(-3) cm(2)/molecules. (C) 2002 Elsevier Science B.V. All rights reserved.