Laboratory Investigation of X-Ray Photolysis of Methanol Ice and Its Implication on Astrophysical Environments

Abstract

Methanol (CH 3 OH) is one of the most abundant organic molecules in astrophysical environments. It has been found in cold regions such as surfaces of comets, ices near young stellar objects and protoplanetary disks, as well as in the gas phase in different regions in space. In this work, we experimentally simulate the methanol ice and its behavior when irradiated by broadband soft X-rays. The experiments were performed at the Brazilian Synchrotron Facility LNLS/CNPEM, employing a broadband photon beam (6 to 2000 eV). The frozen sample was analyzed in situ by infrared spectroscopy (IR) in simulated astrophysical at different radiation fluences. The results show the formation of several new species such as CO 2 , CO, H 2 O and CH 4 during the photolysis CH 3 OH ice by soft X-rays. We determined effective destruction and formation cross-section, as well as the chemical equilibrium fluence (F E ) and desorption yields. The timescale to reach chemical equilibrium in some astrophysical environments with soft X-rays were estimated. The result helps us to understand the photolysis induced by X-rays in organic-rich ices in space environments.

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

“…Such behavior is also observed in the irradiation of other ices by different ionizing sources (e.g. Pilling et al 2019Pilling et al , 2010Vasconcelos et al 2017;Rachid et al 2017;Freitas & Pilling 2020).…”

“…As discussed in details in several previous papers (see, e.g. Andrade et al 2013;Portugal et al 2014;Freitas & Pilling 2020), different bonds have different sensitivity to radiation-induced processes. This indicates that the effective cross section calculated by such bonds depends on the considered bond.…”

Photolysis of CH3CN Ices by Soft X-rays: Implications for the Chemistry of Astrophysical Ices at the Surroundings of X-ray Sources

“…Subtracted integrated absorbance as a function of photon fluence. Red curves are the best fit considering an associative exponential. , Panel a depicts formation cross sections for daughter species formed in the ice, while panel b shows the destruction cross sections for father bonds.…”

“…Figure shows several values for the destruction (or dissociation) cross section for different molecules obtained from X-ray irradiation experiments (employing gas-phase molecules and ices). For gas-phase molecules, time of flight PEPICO spectroscopy was employed, ,− and for ices, the same methodology and instrumentation employed in this work were used; ,,,,− however, some of those are for ice mixtures. Acetone cross section values are related to destruction of three different bond breaks (CO, CH 3 , and CC).…”

“…Red dashed one corresponds to an experiment also using broad-band X-rays, but not using infrared technique to study radiation products. References: a Almeida et al, b Carvalho and Pilling, c Freitas and Pilling, d Pilling and Bergantini, e Rachid et al, f de Souza Bonfim et al, g Fantuzzi et al, h Boechat-Roberty et al, i Pilling et al, j Boechat-Roberty et al, and l Pilling et al…”