The adsorption of NO and the coadsorption of NO and NH3 on Pt(111) has been studied with TDS, work function measurements and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). Pure NO was found to be adsorbed upright at low coverages (theta(NO) < 0.25) with a bond length of 1.24 +/- 0.05 Angstrom which corresponds to an elongation by 0.1 Angstrom as compared to the gas phase. An additional tilted species forms at high coverages. The formation of a coadsorption complex of NH3 and low coverage NO shows up in an elongation of NO to 1.28 +/- 0.05 Angstrom. In the coadsorption complex NO is adsorbed upright. The formation of such a complex which is held together by strong attractive interactions explains the high abundance of the mixed (NN)-N-14-N-15 reaction product in experiments with isotopically labeled educts in the NO + NH3 reaction.