Chemisorption of NO on Rh/Al2O3 surfaces has been examined by FT-IR. The spectra are assigned to two forms of Rh(NO) as well as the Rh(NO)2 species. Apparent interconversion of the linear nitrosyl and dinitrosyl complexes is readily observed at room temperature. The dinitrosyl complex is characterized both by an invariant ratio of 1743- and 1825-cm-1 asymmetric and symmetric stretch bands with coverage and by isotopic data in 15NO and the mixed 14NO and 15NO systems. Force constants for NO stretching motions and for NO/NO ligand interactions on Rh(NO)2 have been used to successfully calculate the experimentally observed spectrum for the mixed isotope, dinitrosyl species. Thermal desorption data and displacement of adsorbed NO with CO are also reported. © 1985 American Chemical Society.