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Mechanisms for the electron-induced degradation of poly(methyl methacrylate) (PMMA) and Kapton polyimide (PMDA-ODA), both of which are commonly used in aerospace applications, were examined over a temperature range of 10 K to 300 K under ultra high vacuum (∼10(-11) Torr). The experiments were designed to simulate the interaction between the polymer materials and secondary electrons produced by interaction with galactic cosmic ray particles in the near-Earth space environment. Chemical alterations of the samples were monitored on line and in situ by Fourier-transform infrared spectroscopy and mass spectrometry during irradiation with 5 keV electrons and also prior and after the irradiation exposure via UV-vis. The irradiation-induced degradation of PMMA resulted in the formation and unimolecular decomposition of methyl carboxylate radicals (CH(3)OCO) forming carbon monoxide (k = 4.60 × 10(-3) s(-1)) and carbon dioxide (k = 1.29 × 10(-3) s(-1)). Temperature dependent gas-phase abundances for carbon monoxide, carbon dioxide, and molecular hydrogen were also obtained for the PMMA and Kapton samples. The lower gas yields detected for irradiated Kapton were typically one or two orders of magnitude less than PMMA suggesting a higher degradation resistance to energetic electrons. In addition, UV-vis spectroscopy revealed the propagation of conjugated bonds induced by the irradiation of PMMA and indicated a decrease in the optical band gap by an increase in absorbance above 500 nm in irradiated Kapton.

The irradiation of pure molecular oxygen (O(2)) and carbon dioxide (CO(2)) 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 (O(3)) in irradiated oxygen ice; and ozone, carbon monoxide (CO), and cyclic carbon trioxide (c-CO(3)) in irradiated carbon dioxide. In addition to these irradiation products, evolution of gas-phase molecular hydrogen (H(2)), atomic helium (He) and molecular oxygen (O(2)) 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, S(e), and nuclear, S(n), 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 5 keV electrons) which showed a surprising correlation between the molecular yields (∼10(-3)-10(-4) 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 (∼10(-2)-10(-3) molecules eV(-1)) than exposure to the ions. Implications of these findings to Solar System chemistry are also discussed.

Pure, crystalline acetonitrile (CHCN) and propionitrile (CHCHCN) particles were formed in a collisional cooling cell allowing for infrared (IR) signatures to be compiled from 50 to 5000 cm. The cell temperature and pressure conditions were controlled to simulate Titan's lower atmosphere (80-130 K and 1-100 mbar), allowing for the comparison of laboratory data to the spectra obtained from the Cassini-Huygens mission. The far-IR features confirmed the morphology of CHCN aerosols as the metastable β-phase (monoclinic) ice, however, a specific crystalline phase for CHCHCN could not be verified. Mie theory and the literature complex refractive indices enabled of the experimental spectra to be modelled. The procedure yielded size distributions for CHCN (55-140 nm) and CHCHCN (140-160 nm) particles. Effective kinetic profiles, tracing the evolution of aerosol band intensities, showed that condensation of CHCHCN proceeded at twice the rate of CHCN aerosols. In addition, the rate of CHCHCN aerosol depletion via lateral diffusion of the particles from the interrogation volume was approximately 50% faster than that of CHCN. The far-IR spectra recorded for both nitrile aerosols did not display absorption profiles that could be attributed to the unassigned 220 cm feature, which has been observed to fluctuate seasonally in the spectra obtained from Titan's atmosphere.

The water amidogen radical complex (H(2)O-NH(2)) is a reactive intermediate in the atmospheric oxidation of ammonia by a hydroxyl radical. In the present study, we identify for the first time the H(2)O-NH(2) complex using matrix isolation infrared spectroscopy. We corroborate our experimental findings with high level coupled cluster ab initio calculations.