Thermal and Photochemistry of Methyl Iodide on Ice Film Grown on Cu(111)

Abstract

Thermal and photochemistry of methyl iodide (CH3I) adsorbed on D2O ice film on Cu(111) at 100 K were studied using temperature-programmed desorption (TPD) time-of-flight mass spectrometry (TOF-MS), X-ray and ultraviolet photoelectron spectroscopies. On the basis of TPD, multilayer and monolayer CH3I molecules desorb from D2O ice layer at 120 and 130 K, respectively. Photo-irradiation at 100 K exhibits dramatic changes in the TPD and I 3d5/2 XPS of CH3I on ice film, due to a dramatic dissociation of CH3I. The dissociation is likely activated by solvated electrons transferred from the metal substrate during photo-irradiation. No other photo-initiated reaction products were found within our instrumental detection limit. During photo-irradiation, the CH3I, CH3 and I could be trapped (or solvated) in ice film by rearrangement (and self-diffusion) of water molecules. A newly appeared parent molecular desorption peak at 145 K is attributed to trapped CH3I. In addition, the CH3 and I may diffuse through ice and chemisorb on Cu(111), indicated by TPD and I 3d5/2 XPS taken with photo-irradiation time, respectively. No molecular ejection was found during photo-irradiation at 100 K. The work functions for CH3I/Cu(111), D2O/Cu (111) and CH3I/D2O/Cu(111) were all measured to be about 3.9 eV, 1.0 eV downward shift from that of clean Cu(111).

Photochemistry of CH3I···(H2O)n Complexes: From CH3I···H2O to CH3I in Interaction with Water Ices and Atmospheric Implications

“…18,19 The discovery of primarily methyl iodide (CH 3 I) as potential sources of reactive halogen species during ozone depletion processes 7,8 have motivated investigations of photodissociation of CH 3 I adsorbed on ice. 9,10,20 There have been extensive experimental and theoretical studies on the photodissociation of CH 3 I in the gas phase 21−25 or adsorbed on ice surfaces. 20 In gas phase, 21−25 decomposition along C−I bond (σ*←n) leads to different photoproducts including I 2 .…”

“…Iodine compounds are naturally released mainly from the oceans either by marine metabolisms (i.e., phytoplankton and micro- and macro-algae) or, in the case of inorganic iodine species (HOI and I 2 ), resulting from the reaction between O 3 and iodide in seawater. − Terrestrial sources of iodine species from arid regions are much less important than marine sources, but have been identified as significant O 3 sinks . The measurements performed during field campaigns showed that photochemical processes occurring within the snowpack may alter the atmospheric composition including the iodocarbon content. , The discovery of primarily methyl iodide (CH 3 I) as potential sources of reactive halogen species during ozone depletion processes , have motivated investigations of photodissociation of CH 3 I adsorbed on ice. ,, There have been extensive experimental and theoretical studies on the photodissociation of CH 3 I in the gas phase − or adsorbed on ice surfaces . In gas phase, − decomposition along C–I bond (σ*← n ) leads to different photoproducts including I 2 .…”

Photodissociation of methyl iodide adsorbed on low-temperature amorphous ice surfaces

“…[1][2][3][4] The interactions of adsorbed organic molecules on ice have been investigated using techniques such as temperature-programmed desorption (TPD), 5-7 electron-stimulated desorption, 8 X-ray photoelectron spectroscopy, 9,10 and reflection absorption infrared absorption spectroscopy. 11,12 These studies show that adsorption, diffusion, and desorption of organic molecules depend largely on the morphology of the ice substrate.…”