THE CHEMICAL ADSORPTION OF 1-HEXENE ON RU(0001) STUDIED BY REFLECTION-ABSORPTION INFRARED-SPECTROSCOPY

The chemisorption of 1-hexene on a Ru(0001) surface has been studied u sing reflection-absorption infrared spectroscopy (RAIRS). At 92 K, a v ery low dose of 1-hexene produced a RAIR spectrum consistent with the formation of a di-sigma type complex. On annealing to 100 K. this spec ies started dehydrogenating on the surface, forming a mixture of rotat ional conformers of hexylidyne, [=C-(CH2)(4)-CH3]. A similar result wa s obtained when adsorbing at 100 K, with predominance of the all-trans conformer of hexylidyne for exposure at a high rate. Hexylidyne prove d to be stable up to at least 120 K, although the conformational equil ibrium changed, gradually favouring species with gauche rotations. Bet ween 130 and 290 K, the decomposition products did not produce detecta ble RAIR spectra. Further thermal decomposition into methylidyne was o bserved at 300 K, in contrast with shorter chain alkylidynes previousl y studied on Ru(0001), which decompose via ethylidyne.