Chemical Evolution of a Co Ice Induced by Soft X-Rays

Abstract

We irradiated a pure carbon monoxide ice with soft X-rays of energies up to 1.2 keV. The experiments were performed using the spherical grating monochromator beamline at the National Synchrotron Radiation Research Center in Taiwan, exploiting both monochromatic (at 0.3 and 0.55 keV) and broader energy (0.25-1.2 keV) fluxes. The infrared spectra of the irradiated ices showed the formation of a number of products such as polycarbon monoand dioxides C n O m , and chains containing up to 10 carbon atoms. While a gentle increase in the energy absorbed by the ice sample is reflected by an increase in the column densities of newly born species, such correlation breaks down at very high fluxes. In this regime the production yield falls down sharply by about a factor of 100. The refractory residue obtained in the broad energy irradiation is a "compromise" between those obtained with proton irradiation of C 3 O 2 and CO ices in previous experiments. Finally, we discuss the possible implications for space chemistry

Synthesis of Complex Organic Molecules in Soft X-Ray Irradiated Ices

“…Formation routes, mechanisms responsible for the production of new species, and efficiency of the different energetic processing have contributed to the interpretation of the observed interstellar ice features (Boogert et al 2015). More recently X-ray processing of ice analogues has been studied given its relevance in circumstellar discs around young stars Andrade et al 2010;Ciaravella et al 2012;Jiménez-Escobar et al 2012;Chen et al 2013;Pilling & Bergantini 2015;Ciaravella et al 2016;Jiménez-Escobar et al 2016, 2018. In solar type stars X-ray emission dominates over far extreme ultraviolet emissions for almost one billion year (Ribas et al 2005) penetrating through the disc and reaching inner regions otherwise forbidden to less energetic photons (e.g., Walsh et al 2012).…”

Characterizing Interstellar Medium, Planetary Surface and Deep Environments by Spectroscopic Techniques Using Unique Simulation Chambers at Centro de Astrobiologia (CAB)

“…Our ongoing collaboration with the Palermo Observatory in Italy and the National Central University in Taiwan is devoted to study the effect of X-rays emitted by young stars in the ice. These experiments were conducted in the ISAC setup using a Palermo home-made X-ray source, and later at the National Synchrotron of Taiwan (NSRRC) to increase the flux of soft X-rays [40,44,48,49,50,51,52,53,54,55]. Meanwhile, we employed swift heavy ions provided by the French accelerator GANIL at Caen to reproduce cosmic ray impact in the ice [56].…”

X-ray induced desorption and photochemistry in CO ice

“…X-ray absorption spectroscopy allows to study the presence of species that are undetected in IR spectroscopy, most notably O and O 2 here. Photon-stimulated ion desorption reveals a very large number of desorbing cations, much larger than the number of neutral species detected in the solid phase by IR spectroscopy and TPD 54 .…”

“…The most relevant work to compare with here is the one of Ciaravella et al 54,55 , since it is the only one having studied directly X-ray photochemistry. Using transmission IR spectroscopy and TPD, they found production of several C x (x = 3, 5, 8, 9), C x O (x = 2 -6) and C x O 2 (x = 1, 3, 5, 7) molecules, similar to those we saw in the form of cations.…”