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Astrophysical icy surface simulation under energetic particles and radiation field in formic acid

Abstract:

In this work, the fragmentation, survival, and chemical reactions of formic acid (HCOOH) molecules condensed at 56 K are analyzed using plasma desorption mass spectrometry (PDMS) and photon-stimulated ion desorption (PSID) in an effort to simulate the effects of energetic charged particles (e.g., cosmic rays) and radiation fields on interstellar/cometary ices. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), employing soft X-ray photons (535.1 eV) and energetic ions (∼65 MeV) obtained as 252Cf fission fragments. Mass spectra of positive and negative desorbed ions were obtained using a time-of-flight (TOF) spectrometer, providing information on the fragmentation pattern and abundance of the ionic species released from the icy surface. In both techniques, the major contribution to the released/desorbed ions were positively charged fragments. The production of several series of clusters, some of them with mass/charge ratios of up to 500 u/e, was observed in the PDMS spectra. Comparison between the employed techniques (photon and ion impacts) indicates that the interaction of energetic ions with formic acid ice produces a greater variety of ions than soft X-ray photon impact. This suggests that cosmic rays and high-energy solar wind particles, despite its reduced flux compared to other lower-energy particles, might play an important role in the synthesis of prebiotic molecules. © 2008 American Chemical Society.