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Project Progress

“Laboratory Simulation of KBO Volaitle ices Under Ionizing Radiation: CO-N₂ Ices”

The exposure of icy Kuiper Belt Objects (KBOs) by ionizing radiation was simulated in this case of exposing carbon monoxide–nitrogen (CO-N₂) ices by energetic electrons. The radiation-induced chemical processing was monitored on-line and in-situ via FTIR spectroscopy and quadupole mass spectrometry. Besides the array of carbon oxides being reproduced as in neat irradiated carbon monoxide (CO) ices studied previously, the radiation exposure at 10 K resulted in the formation of nitrogen-bearing species of isocyanato radical (OCN), linear (l-NCN), nitric oxide (NO), nitrogen dioxide (NO₂), plus diazirinone (N₂CO). The infrared assignments of these species were further confirmed by isotopic shifts. The temporal evolution of individual species was found to fit in first-order reaction schemes, prepping up the underlying non-equilibrium chemistry on the formation of OCN, l-NCN, and NO radicals in particular. Also unique to the binary KBO model ices and viable for the future remote detection is diazirinone (N₂CO) at 1860 cm^-1 (2ν₅) formed at lower radiation exposure.

“Formation of Nitric Oxide and Nitrous Oxide in Electron-irradiated H₂¹⁸O/N₂ Ice Mixtures—Evidence for the Existence of Free Oxygen Atoms in Interstellar and Solar System Analog Ices”

We investigated the irradiation of low temperature H₂¹⁸O/N₂ ice mixtures with energetic electrons in an ultrahigh vacuum chamber. The newly formed species, such as nitric oxide (N¹⁸O), nitrous oxide (NN¹⁸O), hydrogen peroxide (H₂¹⁸O₂) and hydrazine (N₂H₄), were identified in the experiments with infrared absorption spectroscopy and mass spectrometry. The results suggest that the unimolecular decomposition of water molecules within water ices at 10 K can lead to the formation of transient, suprathermal oxygen atoms. These oxygen atoms may play an important role in the formation of oxygen-containing biomolecules such as amino acids and sugar, as well as the decomposition of the biomolecules in the ices.

“Formation Formic Acid in Interstellar and Cometary Ices”

The present laboratory study simulated the abiotic formation of carboxylic acids (RCOOH) in interstellar and solar system model ices of carbon dioxide (CO₂)–hydrocarbon mix CnH₂n+2 (n=1–6). The pristine model ices were irradiated at 10 K under contamination-free, ultrahigh vacuum conditions with energetic electrons generated in the track of galactic cosmic-ray particles. The chemical processing of the ices was monitored by a Fourier transform infrared spectrometer and a quadrupole mass spectrometer during the irradiation phase and subsequent warm-up phases on line and in situ in order to extract qualitative (carriers) and quantitative (rate constants and yields) information on the newly synthesized species. Carboxylic acids were identified to be the main carrier, together with carbon monoxide (CO) and a trace of formyl (HCO) and hydroxycarbonyl (HOCO) radicals at 10 K. The upper limit of acid column density at 10K was estimated as much as (1.2±0.1)×10¹⁷ molecules cm⁻² at doses of 17±2 eV molecule⁻¹, or the yield of 39%±4% from the initial column density of carbon dioxide. The temporal column density profiles of the products were then numerically fit using two independent kinetic schemes of reaction mechanisms. Finally, we transfer this laboratory simulation to star-forming regions of the interstellar medium, wherein cosmic-ray-induced processing of icy grains at temperatures as low as 10 K could contribute to the current level of chemical complexity as evidenced in astronomical observations and in extracts of carbonaceous meteorites.

“Formation of D₂-Water and D₂-Carbonic Acid in Oxygen-Rich Solar System Ices via D⁺² Implantation”

Molecular oxygen (O₂) and carbon dioxide (CO₂) ices were irradiated with energetic D⁺² ions to simulate the exposure of oxygen-bearing solar system ices to magnetospheric H⁺² and H+ ions and energetic protons from the solar wind. The experiments provided evidence on the incorporation of the implanted deuterium and inherent formation of D₂-water (D₂O) as well as D₂-carbonic acid (D₂CO₃). In the molecular oxygen ices, the temporal profiles inferred that D₂-water formation followed successive deuterium atom addition to atomic oxygen via a D-hydroxyl radical intermediate in the matrix. In the carbon dioxide ices, D₂-carbonic acid was likely formed via successive deuterium atom reaction with cyclic carbon trioxide. These chemical processes have specific relevance to water formation on outer solar system bodies, such as the icy moons of Jupiter and Saturn, as well as possible implications for the formation of water on the lunar surface.

“Formation of Ozone in Oxygen-Rich Solar System Ices via Ionizing Radiation”

The irradiation of pure molecular oxygen (O₂) and carbon dioxide (CO₂) ices with 5 keV H⁺ and He+ ions was investigated experimentally to simulate the chemical processing of oxygen rich planetary and interstellar surfaces by exposure to galactic cosmic ray (GCR), solar wind, and magnetospheric particles. Deposited at 12 K under ultra-high vacuum conditions (UHV), the irradiated condensates were monitored on-line and in situ in the solid-state by Fourier transform infrared spectroscopy (FTIR), revealing the formation of ozone (O₃) in irradiated oxygen ice; and ozone, carbon monoxide (CO), and cyclic carbon trioxide (c-CO₃) in irradiated carbon dioxide. In addition to these irradiation products, evolution of gas-phase molecular hydrogen (H₂), atomic helium (He) and molecular oxygen (O₂) were identified in the subliming oxygen and carbon dioxide condensates by quadrupole mass spectrometry (QMS). Temporal abundances of the oxygen and carbon dioxide precursors and the observed molecular products were compiled over the irradiation period to develop reaction schemes unfolding in the ices. These reactions were observed to be dependent on the generation of atomic oxygen (O) by the homolytic dissociation of molecular oxygen induced by electronic, Se, and nuclear, Sn, interaction with the impinging ions. In addition, the destruction of the ozone and carbon trioxide products back to the molecular oxygen and carbon dioxide precursors was promoted over an extended period of ion bombardment. Finally, destruction and formation yields were calculated and compared between irradiation sources (including 5keV electrons) which showed a surprising correlation between the molecular yields (~10³–10⁴ molecules eV-1) created by H⁺ and He⁺ impacts. However, energy transfer by isoenergetic, fast electrons typically generated ten times more product molecules per electron volt (~10²–10³ molecules eV^-1) than exposure to the ions. Implications of these findings to Solar System chemistry are also discussed.

“Forming D₂-Water & D₂-Carbonic Acid in Oxygen-Rich Solar System Ices via D₂+Irradiation”

Molecular oxygen (O₂) and carbon dioxide (CO₂) ices were irradiated with energetic D₂+ ions to simulate the exposure of oxygen-bearing solar system ices to magnetospheric H₂+ and H+ ions and energetic protons from the solar wind. The experiments provided evidence on the incorporation of the implanted deuterium and inherent formation of D₂-water (D₂O) as well as D₂-carbonic acid (D₂CO₃). In the molecular oxygen ices, the temporal profiles inferred that D₂-water formation followed successive deuterium atom addition to atomic oxygen via a D-hydroxyl radical intermediate in the matrix. In the carbon dioxide ices, D₂-carbonic acid was likely formed via successive deuterium atom reaction with cyclic carbon trioxide. These chemical processes have specific relevance to water formation on outer solar system bodies, such as the icy moons of Jupiter and Saturn, as well as possible implications for the formation of water on the lunar surface.