Decomposition of Formaldehyde Multilayer Films on Deoxygenated, Oxygenated, and Water-Adsorbed Vanadium Substrates at Cryogenic Temperatures

Abstract

Interactions of thin formaldehyde films with a polycrystalline V substrate were investigated using temperature-programmed desorption and time-of-flight secondary ion mass spectrometry. A multilayer formaldehyde film grows on a deoxygenated V substrate at 70 K after the formation of a reacted layer at the interface. Most molecules in the film disappear at 100 K via interfacial reaction rather than thermal desorption. However, the liberation of possible reaction products such as H2 and CO is depressed at T < 200 K. The reaction of formaldehyde with the deoxygenated V substrate is characterized by C–O bond scission and uptake of the reaction products in subsurface layers. The formaldehyde multilayer decomposition occurs on oxygenated V substrates as well, where methane and ethylene are observed as reaction products at 100 K. Their relative yields depend on the degrees of substrate oxidation. When a multilayer water film is present on the deoxygenated V substrate, hydrogen is liberated together with methane d...