By introducing a new experimental approach, capable of producing macroscopic fluxes of excited reagents, it has been possible to demonstrate the first surface chemical reaction with electronically excited species. We report a quantum yield close to one for dissociative adsorption of electronically excited SO2 Molecules on a surface leading to formation of molecular sulphur. Both the new phenomenon observed and the experimental technique developed may have important perspectives for technological applications. (C) 2007 Elsevier B.V. All rights reserved.