Photodesorption and Photostability of Acetone Ices: Relevance to Solid Phase Astrochemistry

Abstract

Acetone, one of the most important molecules in organic chemistry, also a precursor of prebiotic species, was found in the interstellar medium associated with star-forming environments. The mechanisms proposed to explain the gas phase abundance of interstellar acetone are based on grain mantle chemistry. High energy photons coming from the stellar radiation field of the nearby stars interact with the ice mantles on dust grains leading to photoionization, photodissociation, and photodesorption processes. In this work we investigate the photodesorption and the photostability of pure acetone ices due to soft X-ray impact. Absolute desorption yields per photon impact for the main positive ionic fragments were determined at the O 1s resonance energy (531.4 eV). The photostability of acetone ice was studied by exposure to different irradiation doses with a white beam of synchrotron radiation. The degradation of the ice was monitored by NEXAFS around the O 1s threshold. From this study we determine the photodissociation cross-section to be about 1.5 × 10 −17 cm 2 which allowed us to estimate the half-life for acetone ice in astrophysical environments where soft X-rays play an important role in chemical processes.

Fragmentation dynamics of doubly charged camphor molecule following C 1s Auger decay

“…Investigating such interactions has profound implications in obtaining insights into processes such as radiation damage in biology and the stability of molecular aggregates like ices in interstellar medium. 1,2 When a core-level electron in a molecule is excited, a valence electron fills the core hole resulting in either photoemission or the removal of one or more partner electrons from the system leading to an Auger decay. Auger processes are the dominant multiple ionisation channels in light atoms, even when they are a part of larger aggregates, like molecules.…”

Processing of astrophysical ices by soft X-rays and swift ions

“…The processing of astrophysical ices by ionizing radiation such as soft X-rays and swift ions has been used in laboratory to simulate the effects of energetic photons (e.g. Pilling et al 2009;Chen et al 2013;Pilling et al2011b;Pilling & Bergantini 2015;Jimenes-Escobar et al 2016;Vasconcelos et al 2017c;Bonfim et al 2016;Rachid et al2017;Almeida et al 2014; and references therein) and cosmic rays (e.g. Strazzulla et al 1983;Palumbo 2006;Strazzulla et al 2007;Seperuelo-Duarte et al 2009;Pilling et al 2010aPilling et al , 2010bHijazi et al 2011;Andrade et al 2013;Bergantini et al 2014a;de Barros et al 2014;Mejía et al 2014;Almeida et al 2017).…”

X-ray photolysis of CH$_3$COCH$_3$ ice: Implications for the radiation effects of compact objects towards astrophysical ices

“…Several laboratory investigations have addressed the effects of radiation on pure acetone ice samples; for example, Hudson (2018) used 1 MeV protons to irradiate acetone ice samples at 20K and infrared spectroscopy to study radiation products, thus corroborating and correcting the previous work of Andrade et al (2014). In Almeida et al (2014), authors irradiated acetone ice samples with soft X-rays (0.01 âĂŞ 2000 eV) to determine desorption yields and photodissociation cross-section.…”