LABORATORY STUDIES ON THE FORMATION OF FORMIC ACID (HCOOH) IN INTERSTELLAR AND COMETARY ICES

Journal Article · Thu Jan 20 00:00:00 EST 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/727/1/27· OSTI ID:21567603

Bennett, Chris J; Kim, Yong Seol; Kaiser, Ralf I ^[1]; Hama, Tetsuya; Kawasaki, Masahiro ^[2]

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1. Department of Chemistry, University of Hawaii, Honolulu, HI 96822 (United States)
2. Department of Molecular Engineering, Kyoto University, Kyoto 615-8510 (Japan)

Mixtures of water (H{sub 2}O) and carbon monoxide (CO) ices were irradiated at 10 K with energetic electrons to simulate the energy transfer processes that occur in the track of galactic cosmic-ray particles penetrating interstellar ices. We identified formic acid (HCOOH) through new absorption bands in the infrared spectra at 1690 and 1224 cm{sup -1} (5.92 and 8.17 {mu}m, respectively). During the subsequent warm-up of the irradiated samples, formic acid is evident from the mass spectrometer signal at the mass-to-charge ratio, m/z = 46 (HCOOH{sup +}) as the ice sublimates. The detection of formic acid was confirmed using isotopically labeled water-d2 with carbon monoxide, leading to formic acid-d2 (DCOOD). The temporal fits of the reactants, reaction intermediates, and products elucidate two reaction pathways to formic acid in carbon monoxide-water ices. The reaction is induced by unimolecular decomposition of water forming atomic hydrogen (H) and the hydroxyl radical (OH). The dominating pathway to formic acid (HCOOH) was found to involve addition of suprathermal hydrogen atoms to carbon monoxide forming the formyl radical (HCO); the latter recombined with neighboring hydroxyl radicals to yield formic acid (HCOOH). To a lesser extent, hydroxyl radicals react with carbon monoxide to yield the hydroxyformyl radical (HOCO), which recombined with atomic hydrogen to produce formic acid. Similar processes are expected to produce formic acid within interstellar ices, cometary ices, and icy satellites, thus providing alternative processes for the generation of formic acid whose abundance in hot cores such as Sgr-B2 cannot be accounted for solely by gas-phase chemistry.

• OSTI ID: 21567603
• Journal Information: Astrophysical Journal, Vol. 727, Issue 1; Other Information: DOI: 10.1088/0004-637X/727/1/27; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
CARBON MONOXIDE
COMETS
COSMIC RADIATION
DECOMPOSITION
ENERGY TRANSFER
FORMIC ACID
FORMYL RADICALS
HYDROXYL RADICALS
ICE
INFRARED SPECTRA
INTERSTELLAR SPACE
MASS SPECTROMETERS
TAIL ELECTRONS
WATER
ACYL RADICALS
CARBON COMPOUNDS
CARBON OXIDES
CARBOXYLIC ACIDS
CHALCOGENIDES
CHEMICAL REACTIONS
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
HYDROGEN COMPOUNDS
IONIZING RADIATIONS
LEPTONS
MEASURING INSTRUMENTS
MONOCARBOXYLIC ACIDS
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
RADIATIONS
RADICALS
SPACE
SPECTRA
SPECTROMETERS