M. A. Smith

University of Houston, Houston, Texas, United States

Are you M. A. Smith?

Claim your profile

Publications (7)11.43 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Titan, the moon of Saturn with a thick atmosphere and an active hydrocarbon-based weather cycle, is considered the best target in the solar system for the study of organic chemistry on a planetary scale. Microfluidic devices that employ liquid phase techniques such as capillary electrophoresis with ultrasensitive laser-induced fluorescence detection offer a unique solution for in situ analysis of complex organics on Titan. We previously reported a protocol for nonaqueous microfluidic analysis of primary aliphatic amines in ethanol, and demonstrated separations of short- and long-chain amines down to -20 °C. We have optimized this protocol further, and used it to analyze Titan aerosol analogues (tholins) generated in two separate laboratories under a variety of different conditions. Ethylamine was a major product in all samples, though significant differences in amine content were observed, in particular for long-chain amines (C12-C27). This work validates microfluidic chemical analysis of complex organics with relevance to Titan, and represents a significant first step in understanding tholin composition via targeted functional group analysis.
    Earth and Planetary Science Letters 10/2014; 403:99–107. DOI:10.1016/j.epsl.2014.06.028 · 4.72 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract The discovery of large (>100 u) molecules in Titan's upper atmosphere has heightened astrobiological interest in this unique satellite. In particular, complex organic aerosols produced in atmospheres containing C, N, O, and H, like that of Titan, could be a source of prebiotic molecules. In this work, aerosols produced in a Titan atmosphere simulation experiment with enhanced CO (N(2)/CH(4)/CO gas mixtures of 96.2%/2.0%/1.8% and 93.2%/5.0%/1.8%) were found to contain 18 molecules with molecular formulae that correspond to biological amino acids and nucleotide bases. Very high-resolution mass spectrometry of isotopically labeled samples confirmed that C(4)H(5)N(3)O, C(4)H(4)N(2)O(2), C(5)H(6)N(2)O(2), C(5)H(5)N(5), and C(6)H(9)N(3)O(2) are produced by chemistry in the simulation chamber. Gas chromatography-mass spectrometry (GC-MS) analyses of the non-isotopic samples confirmed the presence of cytosine (C(4)H(5)N(3)O), uracil (C(5)H(4)N(2)O(2)), thymine (C(5)H(6)N(2)O(2)), guanine (C(5)H(5)N(5)O), glycine (C(2)H(5)NO(2)), and alanine (C(3)H(7)NO(2)). Adenine (C(5)H(5)N(5)) was detected by GC-MS in isotopically labeled samples. The remaining prebiotic molecules were detected in unlabeled samples only and may have been affected by contamination in the chamber. These results demonstrate that prebiotic molecules can be formed by the high-energy chemistry similar to that which occurs in planetary upper atmospheres and therefore identifies a new source of prebiotic material, potentially increasing the range of planets where life could begin. Key Words: Astrochemistry-Planetary atmospheres-Titan-Astrobiology. Astrobiology 12, 809-817.
    Astrobiology 08/2012; DOI:10.1089/ast.2011.0623 · 2.51 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Groups of peaks with mass spacing of ∼13.5 are observed in all of the tholin spectra. Analysis of the Orbitrap tholin measurements indicates that these groups EPSC Abstracts Vol. 6, EPSC-DPS2011-1627, 2011 EPSC-DPS Joint Meeting 2011 c Author(s) 2011 can be defined by molecules that have a constant number of heavy atoms (C+N). The average number of C, N, and H atoms in each group increases linearly as a function of increasing mass. These trends can therefore be extrapolated to the higher masses observed in the CAPS measurements as a first estimate of the possible composition of those molecules. The spacing appears to be a consequence of the degree of saturation of the molecules. The INMS spectra and the CAPSIBS (positive ions) spectra exhibit groups of very regularly spaced peaks as well. The spacing in the INMS data is ∼12.5 but seems to increase towards 13.5 for the heavier masses in the CAPS-IBS data. The spacing change may be indicative of the transition from gas phase molecules to aerosols.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The observations by the Cassini Ion Neutral Mass Spectrometer (INMS) and the Cassini Plasma Spectrometer (CAPS) clearly demonstrate the importance of complex organic chemistry in the upper atmosphere of Titan; a complex coupling of neutral and ion chemistry for organic aerosol generation induced by EUV photons and Saturn's magnetospheric charged particles. To understand the dominant energy source for aerosol formation and its formation chemistry, we comparatively investigate the chemical mechanism in N2/CH4 gas mixtures resulting from EUV-VUV synchrotron radiation (50-150 nm) and tunable mono-energetic electron beam irradiation (5 eV - 2000 eV). These excitation energy sources cover the dominant energy source available in Titan's upper atmosphere. Our previous study of the EUV-VUV photolysis of N2/CH4 gas mixtures revealed the unique role of nitrogen photoionization in the catalytic formation of complex hydrocarbons and in the major nitrogen fixation process in Titan's upper atmosphere (Imanaka and Smith, 2007, 2009, 2010). However, relative roles of ion-molecule reactions and radical/neutral reactions in such complex chemistry remain to be determined. We characterized the electron energy distribution by conducting the Langmuir probe measurements. Degradation of the primary photoelectron from N2 photoionization at 20.6 eV photons is clearly observed, and the electron density rapidly decreases down to 109-10 cm-3, which suggests the complex coupling of ion-molecular reactions and dissociative ion-electron recombination reactions for the observed development of complex organic molecules. The electron beam irradiation experiments at energy larger than 200 eV shows distinct gaseous product distribution with nitrogenated gaseous species from those with EUV irradiation products. The generation of secondary electrons and multiple inelastic collisions of fast electrons might increases the nitrogen fixation efficiency. The much less stringent spin selection rules could provide many additional chemical pathways not open to optical absorption processes. We acknowledge support from the NASA grants NNX08AO13G, NNX09AM95G, NNX10AF08G, and the NAI program.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The large abundance of NH3 in Titan's upper atmosphere is a consequence of coupled ion and neutral chemistry. The density of NH3 is inferred from the measured abundance of NH4+. NH3 is produced primarily through reaction of NH2 with H2CN, a process neglected in previous models. NH2 is produced by several reactions including electron recombination of CH2NH2+. The density of CH2NH2+ is closely linked to the density of CH2NH through proton exchange reactions and recombination. CH2NH is produced by reaction of N(2D) and NH with ambient hydrocarbons. Thus, production of NH3 is the result of a chain of reactions involving non-nitrile functional groups and the large density of NH3 implies large densities for these associated molecules. This suggests that amine and imine functional groups may be incorporated as well in other, more complex organic molecules.
    Faraday Discussions 01/2010; 147:31-49; discussion 83-102. DOI:10.1039/C004787M · 4.19 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Experimental simulations of the initial steps of the ionic chemistry occurring in the ionosphere of Titan were performed at the synchrotron source Elettra in Trieste. The measurements consisted in irradiating with a monochromatic beam of variable wavelength (from the methane ionization edge at 12.6 eV, up to the molecular nitrogen dissociative ionization edge, beyond 24.3 eV) 3 gas mixtures of increasing complexity. The resulting ionic chemistry was recorded by means of a high-resolution ion trap. Experimental results give conclusive information on the validity of ion-chemistry reaction rates used to perform kinetic simulations, but reveal as well new processes, never described earlier. These will be discussed and compared to model results.
  • Cambridge University Press.