Physisorption of metal carbonyls on Cu(100)

Chromium hexacarbonyl (Cr(CO)(6)) and cyclopentadienyl rhodium dicarbonyl ((eta(5)-C5H5)Rh(CO)(2)) were physisorbed on the Cu(100) surface and their molecular orientations were deduced from their reflection-absorption infrared (RAIR) spectra No thermal decomposition of the compounds was observed Physisorbed Cr(CO)(6) exhibited a substantial degree of dipole-dipole coupling within the adlayer, which was successfully disrupted by coadsorption in Ar at 23 K. The large absorption coefficient of the T-1u mode and the different boundary conditions of this ultrathin layer on a surface resulted in the observation of the longitudinal optical mode, confirming that the molecule is oriented with one carbonyl group adjacent to the surface. A Lyndane-Sachs-Teller splitting of 75 cm(-1) was observed for the T-1u mode. The physisorbed layer of (eta(5)-C5H5)Rh(CO)(2) did not exhibit strong dipole-dipole coupling, and was oriented with the C5H5 (Cp) ring parallel to the surface.