Photochemistry of molecules at confined environment: CD3Br/O/Ru(001) and CO2@Ice

Abstract

AbstractThe photochemistry of molecules constrained within a confining environment on surfaces has been studied. Orientation of methyl bromide could be controlled methyl down or up by varying the pre‐adsorbed oxygen coverage due to electrostatic interactions on Ru(001) under UHV conditions. Irradiation of the coadsorption system at 193 nm has shown that the resulting photochemical activity is sensitive to the molecular orientation. Photodesorption and dissociation cross sections were 1.0·10−19 cm−2 for methyl‐down and 3.0·10−19 cm−2 for the methyl‐up configurations. This observation represents the first report of the steric effect in electron‐molecule interaction due to the dissociative electron attachment mechanism of photochemical processes on surfaces.A second system of CO2 molecules caged within ice has also been studied. Here the trapped carbon dioxide molecules cannot leave the surface at their normal desorption temperature near 100 K, but are explosively desorbing at the onset of ice evaporation near 165 K. Upon UV irradiation, enhanced dissociation to adsorbed CO and oxygen is recorded. In addition, a new reactivity channel is observed to form H2CO, tentatively identified as formaldehyde. The relevance of photochemistry of caged molecules within ice to interstellar hydrocarbon formation as a possible route for the origin of life is discussed.