Polyatomic Molecule Synthesis on Dust Grain Analogues Using Superthermal Atoms

Details Polyatomic Molecule Synthesis on Dust Grain Analogues Using Superthermal Atoms Polyatomic Molecule Synthesis on Dust Grain Analogues Using Superthermal Atoms

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sptz.prop50278c&link_type=abstract

Spitzer Proposal ID #50278

Astronomy and Astrophysics

Astrophysics

Scientific paper

This proposal focuses on the physical and chemical processes catalyzed by dust grains that can lead to the formation of larger bio-forming polyatomic molecules through a new experimentally-accessible reaction channel involving fast, ground-state atoms. The fast-atom source at JPL will be used to study molecular formation with well-characterized beams of superthermal H, D, and O atoms (energies of 0.1 to 50 eV) colliding with species frozen (4.8 K) on interstellar dust grain analogues. At these atom-grain energies chemical reaction barriers are overcome and new reaction channels are opened. Simulated are conditions in prestellar cores, YSOs, circumstellar envelopes, cool dark clouds, and protoplanetary disks; from shock-heated regions to cooler and UV-shielded nebulae in the accretion phase. The results of this work will allow one to explain the presence, within these objects, of molecules such as CO2, CH3OH, and H2CO with abundances in excess of that predicted from gas-phase or thermal (closed-channel) gas-grain collisions alone. The laboratory-generated species will be compared to those detected by the Spitzer IRS. One can then correlate the superthermal-atom reactions in the laboratory to the presence of polyatomic species in those astrophysical objects that can harbor superthermal atoms. Predictions can be made, and heretofore undetected absorption/emission lines can be searched. Polyatomic formation has recently been demonstrated at JPL by creating abundant CO2 molecules via the reaction O(3P) + CO(adsorbed at 4.8 K) --> CO2, at O(3P) energies of 2, 5, 10, and 14 eV. The CO2 was detected using temperature-programmed desorption/mass spectrometry. This is the first observation anywhere of molecule production using superthermal atoms. Methanol (CH3OH) and ethanol (CH3CH2OH) have also been synthesized in the system O+CO/CH4 (mixed ice at 4.8 K). This work will be expanded to study formation of H2CO, HCOOH (formic acid), CH3NH2 (methyl amine) and the simplest amino acid CH2NH2COOH (glycine).

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