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

The effect of X-ray irradiation on methanol molecules (CH3OH, CD3OH, and (CH3OH)-C-13) isolated in solid noble gas matrices (Ne, Ar, Kr, and Xe) was studied by FTIR spectroscopy at 6 K. CH2OH center dot, H2CO, HCO center dot 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 center dot 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.