Bonding configurations of the isoelectronic molecules, CO, CH3NC and CH3CN on Pt(111)

The adsorption and reactivity of the isoelectronic molecules CO, CH₃NC and CH₃CN on Pt(111) have been studied by high resolution electron energy loss spectroscopy (EELS) and thermal desorption spectroscopy (TDS). In this way, it has been shown that CO and CH₃NC both adsorb initially in a terminal configuration which at higher coverages coexists with a bridge-bonded form. While CO desorbs molecularly, CH₃NC decomposes at > 400 K to H₂ and HCN. At high coverages a low level of isomerization to the more stable CH₃CN is also seen at 430 K. CH₃CN adsorbs weakly and reversibly in an η²-configuration with an imine-like CN bond. The relationship of these configurations to the chemically important frontier molecular orbitals is addressed.