Bonding and reactivity of acetonitrile on W(100)-(5×1)-C

Abstract

The structures of absorbed acetonitrile and the surface intermediate resulting from the formation of an N–H bond and the cleavage of one C–H bond on W(100)-(5×1)-C under ultrahigh vacuum conditions have been investigated using high resolution electron energy loss and x-ray photoelectron spectroscopies. At temperatures below 200 K, a weakly bound molecular state and a species with a strongly perturbed C–N bond are present on the surface. The molecular state coordinates to a single tungsten atom via the nitrile nitrogen and undergoes competing desorption and reaction below 400 K. Acetonitrile is hydrogenated at the nitrile nitrogen and dehydrogenated at the methyl carbon to form a CH2CNH surface intermediate in the temperature range of 200–400 K in the competing reaction. The C–N stretching frequency for the RCNH intermediate is approximately 1400 cm−1 corresponding to a weakening of the C–N bond proposed to result from bonding of both the nitrile carbon and nitrogen to the surface. The RCNH intermediate reacts further above 400 K. Gaseous acetonitrile is reformed in the range of 400–600 K with competing irreversible decomposition yielding gaseous H2, HNC( HCN) and surface carbon and nitrogen. The acetonitrile formation is proposed to result from an intramolecular isomerization of the CH2CNH on the surface. Only atomic carbon and nitrogen are present on the surface after heating to 700 K.