Destruction of formic acid by soft X-rays in star-forming regions

Astrophysics, abstract
astro-ph/0505082

From: Sergio Pilling [view email]

Date: Wed, 4 May 2005 18:36:08 GMT   (184kb)

Formic acid is much more abundant in the solid state, both in interstellar
ices and cometary ices, than in the interstellar gas (ice/gas ~ 10^{4}) and
this point remains a puzzle. The goal of this work is to experimentally study
ionization and photodissociation processes of HCOOH (formic acid), a glycine
precursor molecule. The measurements were taken at the Brazilian Synchrotron
Light Laboratory (LNLS), employing soft X-ray photons from toroidal grating
monochromator TGM) beamline (200 – 310 eV). Mass spectra were obtained using
photoelectron photoion coincidence (PEPICO) method. Kinetic energy
distributions and abundances for each ionic fragment have been obtained from
the analysis of the corresponding peak shapes in the mass spectra.
Photoionization and photodissociation cross sections were also determined. Due
to the large photodissociation cross section of HCOOH it is possible that in
PDRs regions, just after molecules evaporation from the grain surface, formic
acid molecules are almost totally destroyed by soft X-rays, justifying the
observed low abundance of HCOOH in the gaseous phase. The preferential path for
the glycine formation from formic acid may be through the ice phase reaction.

Keywords: HCOOH; Photoionization; X-rays; Astrochemistry.

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