The adsorption of dinitrogen in the presence of dihydrogen over supported rhodium catalyst films has been studied at pressures up to 8000 Torr using infrared spectroscopy as the analytical probe. The integrated area of the Rh-N-2 band at 2248-2258 cm(-1) has been employed to estimate coverages and adsorption equilibrium constants as a function of temperature. These data were used to determine enthalpies and entropies of adsorption for the Rh-N-2 species. It was found that the presence of Rh-H species coadsorbed with the Rh-N-2 species caused intensity enhancement of the Rh-N-2 infrared band, a blue shift in its frequency, increased coverage of N-2 relative to a Rh-H-free surface, and a stronger interaction of N-2 With Rh. Two forms of hydrogen interacting with Rh appear to be important in causing these observations-a weakly-bound reversible form with a Rh-H infrared band at 2013 cm(-1) and a strongly-bound form postulated by others which has no detectable infrared band. It was also observed that the support TiO2 induced stronger N-2 interaction with Rh than did Al2O3; the trend referred to above concerning coadsorbed Rh-H was observed for both supports.