The chemistry of methyl iodide on Mo(100): formation and reaction of adsorbed methyl species

Abstract

The adsorption of methyl iodide is studled on Mo (100) where ultraviolet photoelectron spectroscopy shows that the methyl lo&de thermally decomposes to form methyl species on warming to ~200 K This self-hydrogenates to yMd methane which desorbs at ~230 K and predosmg the surface with deuterium forms essentially only CH3D lndxcatmg that the methyl species reacts with adsorbed hydrogen and that there is httle H-D exchange This methane desorptlon temperature is identical to that found when methylene species are grafted on the surface by adsorbmg methylene iodide m&catmg that methyl hydrogenation to methane is the rate-hmmng step This temperature is substantmlly lower than that at which methyl and methylene species yield methane from dean and oxygen-covered Mo(100) when formed by other routes It is proposed that this is due to the effect of relatively large iodine atoms adsorbed m the four-fold hollow site affecting neighboring (either atop or bridge) sites

An Investigation of the Reaction Pathway for Ethylene Hydrogenation on Pd(111)

“…[4][5][6] Infrared data were collected from a palladium single crystal sample mounted in a modified 2 3 / 4 -in. six-way cross equipped with infrared-transparent KBr windows.…”

“…Experiments were carried out in three stainless steel ultrahigh vacuum chambers operating at base pressures of less than1 × 10 -10 Torr following bakeout, and which have been described in detail elsewhere. [4][5][6] Infrared data were collected from a palladium single crystal sample mounted in a modified 2 3 / 4 -in. six-way cross equipped with infrared-transparent KBr windows.…”

“…Experiments were carried out in three stainless steel ultrahigh vacuum chambers operating at base pressures of less than1 × 10 -10 Torr following bakeout, and which have been described in detail elsewhere. − …”

On the Reaction Pathway for the Hydrogenation of Acetylene and Vinylidene on Pd(111)

“…These experiments were carried out in two stainless steel ultrahigh vacuum chambers operating at a base pressure of ∼1 × 10 -10 Torr following bakeout and which have been described in detail elsewhere. , Infrared data were collected from a palladium single crystal mounted in a modified 2 3 / 4 ‘ ‘ six-way cross equipped with KBr infrared-transparent windows. The sample could be resistively heated to ∼1200 K or cooled to 80 K using liquid nitrogen.…”

“…In the second chamber, the sample was mounted to a carousel-geometry manipulator and could be similarly heated to ∼1200 K and cooled to 80 K by thermal contact with a liquid nitrogen filled reservoir . Temperature-programmed desorption data were collected using a heating rate of 7.5 K/s and desorbing species detected using a Dychor quadrupole mass spectrometer interfaced to a PC allowing five masses to be monitored sequentially during the desorption sweep.…”