Infrared spectra of the three aminocarbynes CNH2, CNHCH3, and CN(CH3)(2) attached to Pt, Pt7H6, Pt-2, Pt9H14, and Pt-4 clusters are calculated from density functional theory and compared with the corresponding experimental spectra measured on the Pt(111) surface. The different clusters provide models for adsorption at on-top, twofold bridge, and threefold bridge sites. For the Pt-2 and Pt9H14 models of the twofold bridge site, the calculations successfully reproduce the observed frequency shifts for C-13, N-15, and D substitutions and yield fair agreement with the observed relative intensities. In the case of CNHCH3, the calculations for one of two possible conformers give better agreement with the experimental spectra. No improvement was achieved with the larger Pt9H14 cluster compared with the Pt-2 model, indicating that the differences between the experimental and calculated spectra for the latter cluster were not due to finite cluster size effects. The calculated spectra for the different adsorption site models indicate that the experimental spectra are most consistent with the twofold bridge site. (C) 2003 American Institute of Physics.