Frozen methanol bombarded by energetic particles: Relevance to solid state astrochemistry

Methanol is an important precursor of many complex prebiotic species and is found abundantly, in solid phase, in several astrophysical environments, such as comets and protostars. These environments are, in general, subjected to some form of ionizing particles as cosmic rays, solar wind particles and/or photons. To simulate physico chemical effects of cosmic rays on methanol and to investigate in particular its fragmentation and cluster emission from the solid phase, condensed methanol at 55 K was bombarded with ∼65 MeV heavy ions constituted by ²⁵²Cf fission fragments. Mass spectra of positive desorbed ions were obtained using a time-of-flight Plasma Desorption Mass Spectrometry (PDMS-TOF), giving information on the fragmentation pattern and abundance of the ionic species released from the frozen sample surface. Since and CH₃O⁺ are the most abundant species detected, the hydrogenation and de-hydrogenation of methanol result to be the predominant ionic processes in the methanol surface. Furthermore, the hydrogenation yields emission of the (CH₃OH)_nCH₃ cluster series, while the CH₃O⁺ species does not attach to methanol molecules. The production of other cluster ion series, some of them with mass/charge up to 300 u/e was also analyzed by PDMS.