ADSORPTION AND THERMAL-DECOMPOSITION OF TRANS-BUT-2-ENE ON RU(0001), STUDIED BY RAIRS

The adsorption and thermal decomposition of trans-but-2-ene have been studied on the Ru(0001) surface, using reflection-absorption infrared spectroscopy (RAIRS). The IR spectra of submonolayer coverages adsorbed at 90 K were extremely weak, which is compatible with molecular adsorption into the expected di-sigma species. Further exposure produced a spectrum assigned to a pi-adsorbed species. Continued exposure at 90 K to well above the monolayer saturation level produced spectra attributed to physical adsorption, with the observed frequencies similar to the solid phase spectrum. Heating the monolayer to around 200 K produced a spectrum similar to that of adsorbed but-2-yne bonded to the surface as a di-sigma/pi-complex. This species was stable up to 250 K and, above this temperature, no IR adsorption bands were detectable. This behaviour of trans-but-2-ene contrasts with that of but-1-ene and isobutene, which form alkylidyne rather than alkyne species.