Desorption from methanol ice induced by electrons from solar wind or magnetospheres

This work analyzes the physico-chemical effects due to electron irradiation, as e.g. caused by the solar wind, on pure methanol (CH3OH) ice. Methanol has been detected in gas and condensed phases in several astrophysical environments, such as comets, asteroids, toward star forming regions and molecular clouds. In some of these environments, methanol is the most abundant specie after water ice. The interaction of ionizing agents with methanol ice induces the production of ionized species, leading to the formation of new compounds. In this work, pure methanol ice (at 142 K) was irradiated, in ultra-high vacuum regime, with 800 eV electrons, thus simulating the wind in frozen surfaces. The desorbed ions were analyzed using time-of-flight mass spectrometry. The results show the formation of protonated species, such as (CH3OH)H+, H2COH+, C2H3+ and HCO+. Absolute desorption yields were determined and compared with results available in the literature from similar experiments. The ionic desorption rate is an important parameter in surface chemistry. It is often approximated in chemical evolution models of astrophysical environments, due to the lack of experimental data.