Surface kinetics using line of sight techniques: the reaction of chloroform with Cu(111)

The adsorption of chloroform (CHCl3) on Cu(111) in the temperature range 10 0-480 K has been studied using line of sight sticking probability (LOSSP) m easurements, line of sight temperature programmed desorption (LOSTPD), low energy electron diffraction (LEED), He I ultra-violet photoelectron spectro scopy (UPS) and work function measurements. Chloroform adsorbs molecularly at 100 K with a sticking probability of 0.98 +/- 0.02, the monolayer reacti ng on heating to 170 K to form chemisorbed chlorine and adsorbed ethyne. Th e adsorbed ethyne desorbs at just above room temperature with first order k inetics, an activation energy of 77 +/- 6 kJ mol(-1) and a pre-exponential factor of 10(11 +/- 1) s(-1). The sticking probability of chloroform on cle an Cu(111) at 320 K is 0.23 +/- 0.04, which corresponds to activated adsorp tion at zero coverage with an activation energy of 3.5 +/- 0.7 kJ mol(-1). The initial sticking probability is found to increase slightly for temperat ures above room temperature, and also for temperatures below room temperatu re, while the sticking probability at finite coverage is greatly increased by the presence of the dissociation product, ethyne, on the surface. These observations are explained in terms of activated adsorption at zero coverag e which becomes non-activated at finite coverage due to attractive intermol ecular interactions between adsorbed chloroform molecules, and adsorbed chl oroform and ethyne molecules.