Infrared studies of sub-monolayer methylamine and trimethylamine adsorption on Ni(111)

The adsorption of monomethylamine and trimethylamine on Ni(lll) has been st udied using reflection absorption infra-red spectroscopy (RAIRS). At 110 K, both molecules are found to chemisorb molecularly and to retain their gas- phase symmetries at the surface, Methylamine possesses an adsorption site s ymmetry of C-8 in which the NH2 unit is held parallel to the surface plane and the methyl group is tilted with respect to the surface normal. Trimethy lamine possesses C-3v symmetry upon adsorption, with the c(3) axis aligned along the surface normal. The high sensitivity RAIR data allow a peculiar f eature of methylamines to be probed: the lone pair on the nitrogen gives ri se to inequivalence in the CH bonds of the methyl unit, leading to the crea tion of one much weaker C-H bond that produces a decoupled vibration at an unusually low stretching frequency. (C) 1999 Elsevier Science B.V. All righ ts reserved.