Astronomy and Astrophysics – Astrophysics
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p..83a&link_type=abstract
The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole
Astronomy and Astrophysics
Astrophysics
Scientific paper
Formic acid (HCOOH), has been observed in several astronomical sources such as comets, protostellar ices, dark molecular clouds, and regions associated with stellar formation. In some massive star-forming regions such as Orion KL and W51, HCOOH have been observed. In these regions, the presence of X-ray fields illuminating large portions could trigger the formation of photodissociation regions. Inside dense molecular clouds, cosmic rays are the main source of ionization and dissociation, as they are capable of penetrating these regions and inducing the formation of new molecules. In this work we simulate the effects produced by the soft X-ray photon and cosmic rays on condensed formic acid. The sputtering yields, the destruction rate of HCOOH, and the rate of formation of new molecular species were determined from recorded spectra in situ by Fourier transform infrared spectroscopy. The figure 1a shows the virgin HCOOH spectrum (red) and the spectra of formic acid irradiated up to a final fluence of 1013 ions/cm^2 (blue). The evolution of the column density of the newly formed species from ice as a function of fluences is shown in Fig. 1b. The measured HCOOH sputtering yield was about 10^4 molecules/impact, while the HCOOH destruction cross-section was 1,1 10-13 cm^2. Among the formed species are CO, CO_2, H_2O. Their formation cross section are 5,4 10-14 cm^2, 6,1 10-14 cm^2 and 7,4 10-14 cm^2 respectively. Considering the estimated flux of heavy particles of solar wind and of heavy nuclei cosmic rays, we calculated the typical molecular half-lives of frozen molecules in astrophysical surfaces due the presence of heavy particles. At Earth orbit, t1/2 ~ 9,5 x 10^6 years and assuming that the fluxes of solar wind and energetic solar particles are inversely proportional to 1/r^2, this value can be determined as a function of distance up to the heliopause. In this case: t1/2 ~ 4,0 10^6 years. In addition, the photodesorption yields for positive and negative ions were determined using X-ray photons at 537 eV energy (at Brazilian Synchrotron Light Source) and compared with previous results obtained using different ionization agents, such as electrons, heavy ions and photons at different energies. We also correlate our results to the molecular and ion production in protoplanetary discs.
Andrade Denis
Boduc P.
da Silveira Enio F.
Domaracka Alicja
Rothard Hermann
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