Reactions of Clean Lithium Surfaces with SO₂: Molecular Auger Line-Shape Analysis and Reaction Kinetics^t

The products of the reaction of SO₂ with clean metal surfaces have been examined using Auger electron spectroscopy. The Auger spectra were deconvolved of sample and instrument broadening effects, which allowed for detailed fingerprint spectra of several sulfur oxyanions to be distinguished. At SO₂ pressures less than 1 mtorr, complete dissociation of the SO₂ molecule to form a monolayer of 2:1 Li₂0 and Li₂S is observed. At high SO₂ pressures, an overlayer of Li₂S₂04/Li₂S₂03 is formed on top of the Li₂S/Li₂0 layer. This growth behavior is apparently similar to the growth of multilayers of oxide on transition-metal surfaces. The rate of reaction of SO₂ with the clean Li metal (at low surface coverages) was measured for temperatures between 298 and 357 K. An activation energy of 2–5 kcal/mol was determined for the initial reaction to form the Li₂S/Li₂0 monolayer. A model for the growth and stability of the layer is presented.