Title

Methanol Radiolysis of Astrochemical Interest

Date

2012

Department or Program

Chemistry

Primary Wellesley Thesis Advisor

Christopher Arumainayagam

Abstract

Using infrared reflection absorption spectroscopy (IRAS), we have investigated low-energy (5-20 eV) electron-induced reactions in condensed methanol (CH3OH) under ultrahigh vacuum conditions ( 4 × 10−10 torr). In contrast to temperature programmed desorption (TPD), a post-irradiation technique we have used previously to study methanol radiolysis, IRAS does not require thermal processing prior to product detection. Our goal is to simulate processes which occur when high-energy cosmic rays interact with interstellar and cometary ices, where methanol, a precursor of several prebiotic species, is relatively abundant. The interactions of high-energy radiation, such as cosmic rays (Emax 1020 eV), with matter produces large numbers of low-energy (< 15 eV) secondary electrons, which are thought to initiate radiolysis reactions in the condensed phase. Using IRAS we have found compelling evidence for the formation of ethylene glycol (HOCH2CH2OH), formaldehyde (CH2O), dimethyl ether (CH3OCH3), methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), and the hydroxyl methyl radical (•CH2OH) upon low-energy electron irradiation of condensed methanol at 85 K. We have also identified the same nascent radiolysis products following high-energy ( 900 eV) electron irradiation of condensed methanol, a finding which is consistent with the hypothesis that high-energy condensed phase radiolysis is mediated by low-energy electron-induced reactions. The observed formation of radiolysis products at electron energies below 10 eV demonstrates that electron impact ionization cannot be the sole reaction mechanism. The results of experiments such as ours may provide a fundamental understanding of how complex molecules are synthesized in the interstellar medium and comets.

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