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

The adsorption of monomethylamine and trimethylamine on Ni(lll) has been studied 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 symmetry of C(8) in which the NH(2) unit is held parallel to the surface plane and the methyl group is tilted with respect to the surface normal. Trimethylamine possesses C(3v) symmetry upon adsorption, with the c(3) axis aligned along the surface normal. The high sensitivity RAIR data allow a peculiar feature of methylamines to be probed: the lone pair on the nitrogen gives rise to inequivalence in the CH bonds of the methyl unit, leading to the creation 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 rights reserved.