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.