Adsorption and decomposition of methyl iso-cyanide on Pt(111)

Abstract

CH 3NC adsorption and thermal decomposition on a Pt(111) surface has been studied by high resolution EEL and TD spectroscopies. At 90 K, CH 3NC adsorbs initially in a terminal-bonded configuration characterized by a blue-shifted iso-cyanide stretch at 2265-2240 cm −1. At higher coverages this form co-exists with a second form characterized by an imine-like stretch at 1600–1770 cm −1, increasing with coverage. This form is associated with bridge bonding to adjacent surface platinum atoms. Adsorption is irreversible and. except for multilayer desorption at 135 K, only reaction-limited H 2 (T p = 440–460 K) and HCN (T p = 420–610 K) desorption and. at high coverages, isomerization to CH 3 CN (T p = 430 K) was seen. EEL spectra recorded after heating the adsorbed layer indicated that at lower coverages, the molecular integrity of the adsorbed CH 3NC was completely lost before dehydrogenation occurred. On the other hand, at saturation structural changes in the adsorbed layer corresponded firstly to the onset of dehydrogenation and then. at higher temperatures, to HCN evolution. No spectroscopic evidence for an η 2-bonding configuration was found either at low temperatures or during thermal decomposition. The terminal- and bridged-bonded configurations adopted by CH 3NC have been compared and contrasted with those found with the isoelectronic CO and the isomeric CH 3CN by reference to the chemically important frontier orbitals of these ligand molecules.