Radiation-induced transformations of methanol molecules in low-temperature solids: a matrix isolation study

Abstract

The effect of X-ray irradiation on methanol molecules (CH₃OH, CD₃OH, and ¹³CH₃OH) isolated in solid noble gas matrices (Ne, Ar, Kr, and Xe) was studied by FTIR spectroscopy at 6 K. CH₂OH˙, H₂CO, HCO˙ and CO were found to be the main degradation products. Somewhat unexpectedly, the production of CO is quite prominent, even at low doses, and it strongly predominates in low-polarizable matrices (especially, in neon). This result is explained by inefficient quenching of excess energy in the H₂CO molecules initially generated from methanol. Relatively small amounts of CH₄, CH₃˙ and CO₂ were also observed directly after irradiation. The latter species presumably originates from methanol dimers or methanol–water complexes. The mechanisms of radiolysis and annealing-induced reactions are discussed and possible implications for the astrochemically relevant ices are considered.