VIBRATIONAL-SPECTRA AND THERMAL-DECOMPOSITION OF METHYLAMINE AND ETHYLAMINE ON NI(111)

The bonding and geometry of methylamine (CH3NH2) and ethylamine (CH3CH2NH2) on Ni(111) have been investigated with high-resolution electron energy loss vibrational spectroscopy (HREELS). Both amines adsorb molecularly at 150 K through the nitrogen lone pair. Significant metal-hydrogen interactions in the alkyl chain were indicated by "softened" C-H stretching modes with frequencies shifted to 2660-2680 cm-1. Temperature-programmed desorption (TPD) and HREELS were used to monitor their desorption and thermal decomposition on the Ni(111) surface. Both CH3NH2 and CH3CH2NH2 are dehydrogenated in the temperature range 300-400 K. CH3NH2 is dehydrogenated to HCN at about 330 K, which further decomposes above 360 K. CH3CH2NH2 is dehydrogenated to CH3CN, initially by alpha-C-H bond scission, leading to desorption of that molecule at 350 K. On the basis of our spectra, we propose a mechanism for the dehydrogenation processes of CH3NH2 and CH3CH2NH2 on Ni(111).