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

The effect of X-ray irradiation on methanol molecules (CH3 OH, CD3 OH, and13 CH3 OH) isolated in solid noble gas matrices (Ne, Ar, Kr, and Xe) was studied by FTIR spectroscopy at 6 K. CH2 OH˙, H2 CO, 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 H2 CO 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.