Issue |
A&A
Volume 438, Number 3, August II 2005
|
|
---|---|---|
Page(s) | 915 - 922 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20042588 | |
Published online | 18 July 2005 |
Destruction of formic acid by soft X-rays in star-forming regions
1
Observatório do Valongo, Universidade Federal do Rio de Janeiro, Ladeira Pedro Antônio 43, CEP 20080-090, Rio de Janeiro, Brazil e-mail: heloisa@ov.ufrj.br
2
Instituto de Química, Universidade Federal do Rio de Janeiro, Ilha do Fundão, CEP 21949-900, Rio de Janeiro, Brazil
3
Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, CEP 21941-972, Rio de Janeiro, Brazil
Received:
21
December
2004
Accepted:
1
April
2005
Formic acid is much more abundant in the solid state, both
in interstellar ices and cometary ices, than in the interstellar gas
(ice/gas ) 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.
Key words: astrochemistry / molecular processes / ISM: abundances / ISM: molecules / X-rays: ISM / astrobiology
© ESO, 2005
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