257 nm photoinduced chemistry of methyl iodide adsorbed on MgO(100)

Publisher Website
Google Scholar
Abstract
The 257 nm photochemistry of CD3I adsorbed on MgO(100) has been investigated. The photofragments ejected along the surface normal were probed using resonantly enhanced multiphoton ionization spectroscopy coupled with time-of-flight mass spectrometry. Methyl radicals and atomic iodine fragments in both the ground I(2P3/2)≡I and spin–orbit excited I(2P1/2)≡I* states were observed as direct photofragments produced at the surface. Laser-induced desorption of methyl iodide competes with dissociation at the surface. The total cross section for removal of adsorbed CD3I from the surface at 257 nm is comparable to the gas phase cross section. A significant portion of the atomic iodine fragments remain trapped at the surface with preferential trapping of I*. Additionally, nonresonant I+ and I+2 signals were detected and initially observed to increase as a function of the irradiation time and then decrease with further irradiation. This behavior is shown to be indicative of photoinduced production and photoinduced removal of a surface intermediate. A surface reaction mechanism and the existence of a common precursor resulting from the interaction of adsorbed atomic iodine with adsorbed methyl iodide or methyl iodide clusters is postulated.