Chemical Composition of Gas-Phase Positive Ions during Laboratory

Article Cite This: ACS Earth Space Chem. XXXX, XXX, XXX−XXX

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Chemical Composition of Gas-Phase Positive Ions during Laboratory Simulations of Titan’s Haze Formation Jennifer L. Berry, Melissa S. Ugelow,† Margaret A. Tolbert, and Eleanor C. Browne* Department of Chemistry and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309, United States

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ABSTRACT: The organic haze in the atmosphere of Saturn’s moon Titan affects the moon’s atmospheric and surface properties. Ions are known to play an important role in haze formation chemistry; however, the role of ions in laboratory simulations of haze formation is poorly characterized. Here, we use a high-resolution time-of-flight mass spectrometer with an atmospheric pressure interface to chemically characterize the ambient gas-phase cations formed as haze is produced by the far ultraviolet photolysis of CH4 in N2. These experiments show that the chemical composition of the cations is complex. High molecular weight ions up to m/z 400 are observed, with organic nitrogen ions, including ions with multiple nitrogen atoms, accounting for the majority of the identified ion peaks. Many of the ions identified in this work have been observed in Titan’s upper atmosphere by the Cassini Ion and Neutral Mass Spectrometer. While the chemistry in this study is likely more representative of Titan’s lower atmosphere than of its upper atmosphere, the results presented here suggest that ion composition, including the composition of organic nitrogen ions, may be variable and diverse throughout Titan’s atmosphere. This in turn has potential implications for haze growth and the formation of complex molecules. KEYWORDS: organic nitrogen, organic hazes, Titan, ions, mass spectrometry

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INTRODUCTION Atmospheric hazes are ubiquitous in our solar system, existing on Jupiter,1 Saturn,2 Uranus,3 Neptune,4 Pluto,5 and Saturn’s moon Titan.6 Additionally, geochemical data suggests that early Earth was surrounded by a planetary haze multiple times during the Archean.7,8 Hazes play an important role in determining the chemical and physical processes occurring in the atmosphere and on the surface of planetary bodies. For example, hazes affect the radiative balance of planetary objects, dramatically influencing the temperature of the atmosphere and surface. The organic haze that surrounds Titan is the major contributor to the antigreenhouse cooling effect that reduces the surface temperature by ∼9 K.9 The discoveries of the Cassini−Huygens mission have transformed our understanding of Titan’s haze formation. Instruments on the Cassini orbiter found that haze formation is initiated in the ionosphere by high energy solar photons and high energy particles from Saturn’s magnetosphere that dissociate and ionize N2 and CH4.10−14 Complex ion-neutral chemistry follows, leading to the formation of heavy ions; cations up to m/z 99 and 350 were detected by the Cassini Ion and Neutral Mass Spectrometer (INMS) and the Cassini Plasma Spectrometer/Ion Beam Spectrometer (CAPS/IBS), respectively. Both instruments measured intense ion signals at both even and odd masses separated by m/z 12 and 14, © XXXX American Chemical Society

suggesting that the ions in Titan’s upper atmosphere are composed of carbon, hydrogen, and nitrogen.15,16 In addition, massive negative ions up to m/z 10,000 were detected by the CAPS/Electron Spectrometer.14 The formation of these heavy ions is a key step in haze formation.13,17 Once the haze particles form, their evolution continues throughout their descent in the atmosphere driven by a combination of radical chemistry, surface growth, and coagulation, the relative contributions of which depend on altitude.18,19 To better understand Titan’s haze, haze analogs (tholins) are created in the laboratory. As summarized by Cable et al.,20 various energy sources, ranging from plasma discharge to electron bombardment are used in laboratory experiments to simulate the production of haze in Titan’s upper atmosphere. Synthesized tholins are unsaturated, slightly aromatic compounds containing large amounts of nitrogen with structures similar to nitrogen containing polycyclic aromatic hydrocarbons (NPAHs) or conjugated aromatic imines or nitriles.20 These organic nitrogen molecules are of particular interest as they may have implications for prebiotic chemistry. Prebiotic Received: October 3, 2018 Revised: December 20, 2018 Accepted: December 20, 2018

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DOI: 10.1021/acsearthspacechem.8b00139 ACS Earth Space Chem. XXXX, XXX, XXX−XXX

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ACS Earth and Space Chemistry

Figure 1. Experimental schematic of the laboratory simulation of Titan photochemical haze production coupled to a High-Resolution Time-ofFlight Mass Spectrometer with an Atmospheric Pressure interface (APi-ToF) for ion measurement. The arrows in the sample production schematic designate the direction of flow and the dashed line within the APi-ToF designates the ion path through the two radio frequency-only segmented quadrupoles, lens stack, and high-resolution time-of-flight mass spectrometer.

CH4 in N2 with a FUV source. High-resolution mass spectra were taken with an atmospheric pressure interface mass spectrometer to determine the exact chemical composition of ions at the same nominal mass. By examining the chemical composition of ions formed during the irradiation of two different CH4 concentrations, the connection between haze characteristics and gas-phase ions and neutrals can be explored.

molecules, like amino acids and nucleotide bases, have been detected in haze particles that were formed in mixtures of CH4/CO/N2.21 Amino acids have also been detected following tholin hydrolysis.22,23 Far ultraviolet (FUV) light has also been used to produce tholins24−36 as ultraviolet irradiation is the dominate energy source in Titan’s atmosphere, particularly in the lower atmosphere.18,20 Although FUV is unable to ionize or dissociate N 2, multiple laboratory studies using FUV irradiation of organic precursors in N2, mostly of CH4 in N2, have observed nitrogen incorporation into tholins and gasphase products.26,27,29−36 Specific organic nitrogen compounds identified during the irradiation of CH4 in N2 include nitriles and amines.29,30,32,33,36 Trainer et al.29 and Yoon et al.32 have previously described possible mechanisms for the dissociation of N2. These include the reaction of the CH4 photolysis CH with N2 to form HCN and N. However, this reaction is spin forbidden and has a large activation energy. Thus, the reaction of CH with CH4 will dominate over the reaction with N2.29 Additionally, CH could react with N2 through a termolecular process to form the HNCN radical or the HCN2 radical. Subsequent reactions of these radicals may result in the breaking of the nitrogen bond. The branching ratios of the different reaction pathways and the cross sections of the resulting products are unknown, making it difficult to estimate the contribution of this pathway to nitrogen activation.29 A third possibility includes the reaction of the long-lived atomic N(2D) state with small organic molecules.37,38 However, within our system, the formation of atomic nitrogen through the direction photolysis or predissociation of N2 is unlikely due to the small absorption cross section of N2 around the Lymanα wavelength.29,32 While N(2D) may be formed through the interaction of galactic cosmic rays (GCRs) with N2, this source is unable to account for the magnitude of observed nitrogen incorporation in the system (see detailed discussion in the Results and Discussion section). Thus, the mechanism of nitrogen incorporation into organic molecules under the experimental conditions used here remains uncertain. Ion chemistry is one possible mechanism that has been suggested for nitrogen incorporation.13,15,29 Although ion chemistry is well recognized as an important process for haze formation in the upper atmosphere of Titan, there is a lack of measurements characterizing ion composition in haze simulation experiments. Here, we characterize the chemical composition of cations produced during the irradiation of

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MATERIALS AND METHODS Sample Preparation. The haze generation procedure has been described in detail previously.28,29 Briefly, gas mixtures are formed by mixing ultrahigh purity CH4 (Airgas, 99.99%) and ultrahigh purity N2 (Airgas, 99.999%) or high purity Ar (Airgas, 99.998%) in a stainless-steel mixing chamber for at least 8 h (Figure 1). CH4 mixing ratios were 0.1% or 2% by volume. These ratios were chosen because 0.1% CH4 has previously been shown to be near peak aerosol production for this setup, allowing for a comparison of the gas-phase ion chemistry to previous haze studies,28,31,39 and 2% CH4 is representative of Titan’s stratosphere. After mixing, the gas mixture is flowed from the mixing chamber into the FUV glass reaction cell at 100 sccm, controlled by a mass flow controller (Mykrolis, FC-2900). A deuterium lamp (Hamamastsu, L1825), emitting between 115 to 400 nm with a strong peak intensity at the Lyman-α line and attached to the FUV reaction cell, initiates the haze production at ambient pressure and temperature (∼840 mbar and 20 °C). The flux of the lamp has been previously measured as 1014 photons cm−2 s−1.28,32 Residence time in the cell is around 3 min. The reacted gas mixture and haze particles exit the cell and combine with ∼600 sccm ultrahigh purity N2 or high purity Ar to provide sufficient flow for the ion chemical composition measurements. Analysis of the experiment is divided into four sections, an hour background with the lamp off, a 25 min period beginning when the lamp was turned on and warming up (warm up), a 30 min period of lamp stability (lamp on), and a 30 min period after the lamp was turned off (cool down). APi-ToF. A High-Resolution Time-of-Flight Mass Spectrometer with an Atmospheric Pressure interface (APi-HRToF-MS, hereafter APi-ToF; Aerodyne Research, Inc. and Tofwerk AG)40 measures the chemical composition of gaseous cations formed during photochemical haze production in the FUV reaction cell. There is no active ionization method in the APi-ToF, and thus, only ambient ions are measured. The B


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Figure 2. Example of fully constrained high resolution peak fitting for the averaged lamp on mass spectrum (25 min) of 2% CH4 in N2. (a,b) Examples of fitting to multiple peaks at the same nominal mass and (c) example of fitting to an isolated ion.

Figure 3. Time series of total ion count (TIC) and CxHyNw+ ions during the photolysis of 2% CH4 in N2. Ion counts were averaged for 5 min with the symbol indicating the middle of the averaging period.

spectra are analyzed in two mass regions. The spectra are divided into low and high regions (separated at m/z 50), analyzed, and recombined after high-resolution peak fitting. By constraining peak shape and peak width in time-of-flight space, signals from overlapping peaks at the same nominal mass are fit and exact chemical formulas are assigned (Figure 2).41−43 No correction for the m/z-dependent ion transmission efficiency is applied,44 and thus, intensity of signals across the mass axis cannot be compared quantitatively. Intensity changes for a given ion, however, are proportional to absolute changes.

products formed in the cell are directly sampled by the APiToF; the mixture at no point is exposed to Earth’s atmosphere. Although anions can also be measured with the APi-ToF, cation and anion measurements cannot be made simultaneously, and this work focuses only on cation measurements. In the APi-ToF, ions are sampled through three sequential, differentially pumped chambers: two radio frequency-only segmented quadrupoles followed by a lens stack (Figure 1). These regions focus and guide the ions to the orthogonal extraction region of the high-resolution time-of-flight mass spectrometer, while neutrals are pumped away. The voltages within the quadrupoles are tuned to favor transmission of intact ion−molecule clusters; however, evaporation of weakly bound clusters as they enter the vacuum region is expected. Mass spectra were collected with a mass range of m/z 1−707 and 10 s resolution. This instrument has high mass resolving power (∼7000 m/z/Δ(m/z)) and high mass accuracy ( 100. Pre-Cassini models predict, however, that the gasphase ions are predominantly hydrocarbon cations,77−79

our comparison on the chemical characteristics of the ions rather than on ion abundance. We compare the ions using Kendrick Mass Defect analysis (Figure 6). A table comparing the exact species in the APi-ToF measurements with the INMS assignments is provided in Table S1. The Kendrick Mass is calculated by redefining the exact mass of 12CH2 as its nominal mass: ji M nominal CH2 mass yzz zz exact Kendrick Mass = IUPAC mass × jjjj j MIUPAC CH mass zz 2 k {

(1)

and the Kendrick Mass Defect is defined as Kendrick Mass Defect = exact Kendrick Mass − nominal Kendrick Mass

(2)

The advantage of this analysis is that, when high-resolution mass information is available, such as with the APi-ToF measurements, the Kendrick Mass Defect analysis can be performed without a molecular formula assignment. Thus, we can include the unidentified ions detected by the APi-ToF in this analysis. In a CH2 Kendrick plot, compounds differing by the addition of CH2 will all have the same mass defect and form a horizontal line in the plot. The mass defect decreases as compounds become more unsaturated. A decrease in mass defect also occurs upon replacement of CH2 with a N atom. As seen by the overlapping points in Figure 6 and identical protonated molecular formulas in Table S1, for low mass ions (m/z < 60), about 54% of the species in the INMS spectra are also measured during our experiment. The majority of the ions that are measured both by the APi-ToF and INMS are CxHy+ ions with x = 2−4 (Figure 6b). There is less overlap between the two measurements for the CxH2x+nNH+ ions (n = −5, −3, −1, 1, and 3); the CxH2x+nNH+ ions measured by the APi-ToF belong to the more saturated families (higher n values), whereas the INMS ions are more unsaturated (lower n values). The exception is the nitrile family (n = −1), which is measured by both instruments. Many of the lower mass INMS ions that are not measured in our experiment are present at m/z ≤ 18. Some of this discrepancy may be attributable to the poor ion transmission of the APi-ToF in that mass range. The other ions not detected in our experiment, but measured by INMS, are typically highly unsaturated organic or organic nitrogen ions including some odd electron ions. Above m/z 60, the APi-ToF data are characterized by several horizontal lines related by the addition of CH2 that are absent in the INMS and CAPS/IBS assignments. Instead, the INMS and CAPS/IBS ions rapidly become unsaturated as illustrated by the increasingly negative mass defects as m/z increases. In contrast, the APi-ToF ions begin to increase in unsaturation at higher m/z values, consistent with the CH2 family analysis presented in Figure 6. Due to the low resolution of the CAPS/IBS measurements, the high m/z assignments are approximate in nature. While many of the CAPS/IBS ions are believed to be aromatic hydrocarbons, ions observed less frequently are also attributed to nitrile polymer ions containing multiple nitrogen atoms.16 Our work found that a large number of the organic nitrogen ions (30% from the 2% CH4/N2 experiment) contained >1 nitrogen. Similar to the lower m/z results, the high m/z ions with multiple nitrogen atoms observed in our work are more saturated than the CAPS/IBS interpretation. G


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ACS Earth and Space Chemistry although the results likely reflect the limited knowledge of neutral species prior to Cassini measurements. A more recent model of coupled ion-neutral photochemistry reports that in the lower atmosphere, GCR ionization produces major cation species that are both nitrogen-bearing and hydrocarbon ions.80 C3H7NH+, C5H5NH+, C6H9+, C6H11+, and C7H9+ are the major species in the lower atmosphere according to this model of which only C3H7NH+ was detected by the APi-ToF in this study. Additionally, in the modeled work the CxHy+ ions have a similar intensity to CxHyN+ ions.80 Model predictions of Titan’s lower atmospheric ion composition stand in contrast to our measurements that show the cations are dominated by nitrogen containing organics and that CxHy+ ions contribute minimally to the observed spectra. In Titan’s lower atmosphere, GCRs are important in the chemistry of nitrogen-bearing compounds,80,81 but as discussed earlier, ionization by GCRs cannot explain the magnitude of nitrogen incorporation observed in our work. As the mechanism of nitrogen incorporation into organic nitrogen compounds with this FUV energy source is currently not understood, evaluation of the exact chemical process leading to these ions as well as an assessment of the potential importance of this process on Titan is currently not feasible, preventing it from being added to current models. However, if similar chemistry occurs on Titan, our results suggest that the chemical composition of ions in Titan’s lower atmosphere is influenced by processes missing from current models. Since hydrocarbons, nitriles, and amines have been found to be strongly impacted by ion chemistry,70 understanding how organic nitrogen ions are formed in these experiments may prove to be important for future Titan atmospheric models.

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AUTHOR INFORMATION

Corresponding Author

*Tel: (303)735-7685. E-mail: [email protected]. ORCID

Eleanor C. Browne: 0000-0002-8076-9455 Present Address †

NASA Goddard Space Flight Center, 8800 Greenbelt Road, MC 691, Greenbelt, MD 20771, USA and University Space Research Association, 7178 Columbia Gateway Drive, Columbia, MD 21046, USA. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS J.L.B. and E.C.B. acknowledge start-up funds provided by the University of Colorado Boulder Department of Chemistry and Cooperative Institute for Research in Environmental Sciences. J.L.B acknowledges additional support from the CU Boulder Summer Departmental Fellowship.

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ABBREVIATIONS APi-ToF, atmospheric pressure interface−high-resolution− time-of-flight−mass spectrometer; CAPS, Cassini plasma spectrometer; DBE, double bond equivalency; FUV, far ultraviolet; GCR, galactic cosmic rays; IBS, ion beam spectrometer; INMS, Ion and Neutral Mass Spectrometer; NPAH, nitrogen containing polycyclic aromatic hydrocarbon; PIT-MS, proton-transfer ion-trap mass spectrometry; TIC, total ion count

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CONCLUSIONS Numerous and chemically diverse gas-phase cations up to m/z 400 were formed during the FUV irradiation of CH4 in N2. Similar to previous studies using this irradiation source, we observed extensive nitrogen incorporation into organic compounds, leading to mass spectra dominated by organic nitrogen ions that became increasingly unsaturated with increasing molecular weight. A large number of species containing more than one nitrogen were also detected, adding the complexity that is necessary for the possible formation of prebiotic compounds. While the impact of ion chemistry on haze formation in this experiment is currently unclear, the formation of high molecular weight, nitrogen-containing ions show that complex chemistry is occurring, which influences the composition of ions. More work investigating the role that this complex chemistry plays in the growth of ions, molecules, and aerosols throughout Titan’s atmosphere is required.

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0.1% CH4 in Ar/N2 (Figure S4); comparison between identification of ions from Titan laboratory simulations and Cassini measurements (Table S1); comparison between PIT-MS and APi-ToF identification (Table S2) (PDF)

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REFERENCES

(1) West, R. A.; Hord, C. W.; Simmons, K. E.; Coffeen, D. L.; Sato, M.; Lane, A. L. Near-Ultraviolet Scattering Properties of Jupiter. J. Geophys. Res. 1981, 86 (A10), 8783−8792. (2) Gillett, F. C.; Forrest, W. J. The 7.5- to 13.5-Micron Spectrum of Saturn. Astrophys. J. 1974, 187, L37−L39. (3) Pollack, J. B.; Rages, K.; Pope, S. K.; Tomasko, M. G.; Romani, P. N.; Atreya, S. K. Nature of the Stratospheric Haze on Uranus: Evidence for Condensed Hydrocarbons. J. Geophys. Res. 1987, 92 (A13), 15037−15065. (4) Baines, K. H.; Smith, W. M. H. The Atmospheric Structure and Dynamical Properties of Neptune Derived from Ground-Based and IUE Spectrophotometry. Icarus 1990, 85 (1), 65−108. (5) Gladstone, G. R.; Stern, S. A.; Ennico, K.; Olkin, C. B.; Weaver, H. A.; Young, L. A.; Summers, M. E.; Strobel, D. F.; Hinson, D. P.; Kammer, J. A.; et al. The Atmosphere of Pluto as Observed by New Horizons. Science 2016, 351 (6279), aad8866. (6) Smith, B. A.; Soderblom, L.; Beebe, R.; Boyce, J.; Briggs, G.; Bunker, A.; Collins, S. A.; Hansen, C. J.; Johnson, T. V.; Mitchell, J. L.; et al. Encounter with Saturn: Voyager 1 Imaging Science Results. Science 1981, 212 (4491), 163−191. (7) Zerkle, A. L.; Claire, M. W.; Domagal-Goldman, S. D.; Farquhar, J.; Poulton, S. W. A Bistable Organic-Rich Atmosphere on the Neoarchaean Earth. Nat. Geosci. 2012, 5 (5), 359−363. (8) Izon, G.; Zerkle, A. L.; Zhelezinskaia, I.; Farquhar, J.; Newton, R. J.; Poulton, S. W.; Eigenbrode, J. L.; Claire, M. W. Multiple Oscillations in Neoarchaean Atmospheric Chemistry. Earth Planet. Sci. Lett. 2015, 431, 264−273.

ASSOCIATED CONTENT

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsearthspacechem.8b00139. Calculation of total ion loss (Section 1); background ionization (Section 2); analysis of control studies (Section 3); background and warm-up averaged mass spectra for 2% CH4 in N2 (Figure S1); CxH2x+nNH+ mass spectrum for 0.1% CH4 in N2 (Figure S2); average mass spectra for the lamp on periods of the Ar control experiments (Figure S3); CxH2x+nNH+ mass spectra for H


Article

ACS Earth and Space Chemistry (9) McKay, C. P.; Pollack, J. B.; Courtin, R. The Greenhouse and Antigreenhouse Effects on Titan. Science 1991, 253 (5024), 1118− 1121. (10) Wahlund, J.-E.; Galand, M.; Müller-Wodarg, I.; Cui, J.; Yelle, R. V.; Crary, F. J.; Mandt, K.; Magee, B.; Waite, J. H.; Young, D. T.; et al. On the Amount of Heavy Molecular Ions in Titan’s Ionosphere. Planet. Space Sci. 2009, 57 (14−15), 1857−1865. (11) Lavvas, P.; Yelle, R. V.; Koskinen, T.; Bazin, A.; Vuitton, V.; Vigren, E.; Galand, M.; Wellbrock, A.; Coates, A. J.; Wahlund, J.-E.; et al. Aerosol Growth in Titan’s Ionosphere. Proc. Natl. Acad. Sci. U. S. A. 2013, 110 (8), 2729−2734. (12) Coates, A. J.; Wellbrock, A.; Lewis, G. R.; Jones, G. H.; Young, D. T.; Crary, F. J.; Waite, J. H.; Johnson, R. E.; Hill, T. W.; Sittler, E. C., Jr. Negative Ions at Titan and Enceladus: Recent Results. Faraday Discuss. 2010, 147, 293−305. (13) Waite, J. H.; Young, D. T.; Cravens, T. E.; Coates, A. J.; Crary, F. J.; Magee, B.; Westlake, J. The Process of Tholin Formation in Titan’s Upper Atmosphere. Science 2007, 316 (5826), 870−875. (14) Coates, A. J.; Crary, F. J.; Lewis, G. R.; Young, D. T.; Waite, J. H.; Sittler, J. C. Discovery of Heavy Negative Ions in Titan’s Ionosphere. Geophys. Res. Lett. 2007, 34 (22), 1−6. (15) Vuitton, V.; Yelle, R. V.; McEwan, M. J. Ion Chemistry and NContaining Molecules in Titan’s Upper Atmosphere. Icarus 2007, 191 (2), 722−742. (16) Crary, F. J.; Magee, B. A.; Mandt, K.; Waite, J. H.; Westlake, J.; Young, D. T. Heavy Ions, Temperatures and Winds in Titan’s Ionosphere: Combined Cassini CAPS and INMS Observations. Planet. Space Sci. 2009, 57 (14−15), 1847−1856. (17) Lavvas, P.; Yelle, R. V.; Koskinen, T.; Bazin, A.; Vuitton, V.; Vigren, E.; Galand, M.; Wellbrock, A.; Coates, A. J.; Wahlund, J.-E.; et al. Aerosol Growth in Titan’s Ionosphere. Proc. Natl. Acad. Sci. U. S. A. 2013, 110 (8), 2729−2734. (18) Lavvas, P.; Sander, M.; Kraft, M.; Imanaka, H. Surface Chemistry and Particle Shape: Processes for the Evolution of Aerosols in Titan’s Atmosphere. Astrophys. J. 2011, 728 (2), 80. (19) Tomasko, M. G.; Doose, L.; Engel, S.; Dafoe, L. E.; West, R.; Lemmon, M.; Karkoschka, E.; See, C. A Model of Titan’s Aerosols Based on Measurements Made inside the Atmosphere. Planet. Space Sci. 2008, 56 (5), 669−707. (20) Cable, M. L.; Hörst, S. M.; Hodyss, R.; Beauchamp, P. M.; Smith, M. A.; Willis, P. A. Titan Tholins: Simulating Titan Organic Chemistry in the Cassini-Huygens Era. Chem. Rev. 2012, 112 (3), 1882−1909. (21) Hörst, S. M.; Yelle, R. V.; Buch, A.; Carrasco, N.; Cernogora, G.; Dutuit, O.; Quirico, E.; Sciamma-O’Brien, E.; Smith, M. A.; Somogyi, Á .; et al. Formation of Amino Acids and Nucleotide Bases in a Titan Atmosphere Simulation Experiment. Astrobiology 2012, 12 (9), 809−817. (22) Khare, B. N.; Sagan, C.; Ogino, H.; Nagy, B.; Er, C.; Schram, K. H.; Arakawa, E. T. Amino Acids Derived from Titan Tholins. Icarus 1986, 68 (1), 176−184. (23) McDonald, G. D.; Thompson, W. R.; Heinrich, M.; Khare, B. N.; Sagan, C. Chemical Investigation of Titan and Triton Tholins. Icarus 1994, 108 (1), 137−145. (24) Tran, B. N.; Joseph, J. C.; Force, M.; Briggs, R. G.; Vuitton, V.; Ferris, J. P. Photochemical Processes on Titan: Irradiation of Mixtures of Gases That Simulate Titan’s Atmosphere. Icarus 2005, 177 (1), 106−115. (25) Tran, B. N.; Joseph, J. C.; Ferris, J. P.; Persans, P. D.; Chera, J. J. Simulation of Titan Haze Formation Using a Photochemical Flow Reactor. The Optical Constant of the Polymer. Icarus 2003, 165 (2), 379−390. (26) Gautier, T.; Sebree, J. A.; Li, X.; Pinnick, V. T.; Grubisic, A.; Loeffler, M. J.; Getty, S. A.; Trainer, M. G.; Brinckerhoff, W. B. Influence of Trace Aromatics on the Chemical Growth Mechanisms of Titan Aerosol Analogues. Planet. Space Sci. 2017, 140, 27−34. (27) Trainer, M. G.; Sebree, J. A.; Yoon, Y. H.; Tolbert, M. A. The Influence of Benzene As a Trace Reactant in Titan Aerosol Analogs. Astrophys. J., Lett. 2013, 766 (L4), 1−5.

(28) Trainer, M. G.; Pavlov, A. A.; DeWitt, H. L.; Jimenez, J. L.; McKay, C. P.; Toon, O. B.; Tolbert, M. A. Organic Haze on Titan and the Early Earth. Proc. Natl. Acad. Sci. U. S. A. 2006, 103 (48), 18035− 18042. (29) Trainer, M. G.; Jimenez, J. L.; Yung, Y. L.; Toon, O. B.; Tolbert, M. A. Nitrogen Incorporation in CH 4 -N 2 Photochemical Aerosol Produced by Far Ultraviolet Irradiation. Astrobiology 2012, 12 (4), 315−326. (30) Hörst, S. M.; Yoon, Y. H.; Ugelow, M. S.; Parker, A. H.; Li, R.; de Gouw, J. A.; Tolbert, M. A. Laboratory Investigations of Titan Haze Formation: In Situ Measurement of Gas and Particle Composition. Icarus 2018, 301, 136−151. (31) Hicks, R. K.; Day, D. A.; Jimenez, J. L.; Tolbert, M. A. Elemental Analysis of Complex Organic Aerosol Using Isotopic Labeling and Unit-Resolution Mass Spectrometry. Anal. Chem. 2015, 87 (5), 2741−2747. (32) Yoon, Y. H.; Hörst, S. M.; Hicks, R. K.; Li, R.; de Gouw, J. A.; Tolbert, M. A. The Role of Benzene Photolysis in Titan Haze Formation. Icarus 2014, 233, 233−241. (33) Cable, M. L.; Hörst, S. M.; He, C.; Stockton, A. M.; Mora, M. F.; Tolbert, M. A.; Smith, M. A.; Willis, P. A. Identification of Primary Amines in Titan Tholins Using Microchip Nonaqueous Capillary Electrophoresis. Earth Planet. Sci. Lett. 2014, 403, 99−107. (34) Sebree, J. A.; Stern, J. C.; Mandt, K. E.; Domagal-Goldman, S. D.; Trainer, M. G. 13C and 15N Fractionation of CH4/N2Mixtures during Photochemical Aerosol Formation: Relevance to Titan. Icarus 2016, 270, 421−428. (35) Dodonova, N. Y. Activation of Nitrogen by Vacuum Ultraviolet Radiation. Russ. J. Phys. Chem. 1966, 40 (5), 523−524. (36) Scattergood, T. W.; McKay, C. P.; Borucki, W. J.; Giver, L. P.; van Ghyseghem, H.; Parris, J. E.; Miller, S. L. Production of Organic Compounds in Plasmas: A Comparison among Electric Sparks, LaserInduced Plasmas, and UV Light. Icarus 1989, 81 (2), 413−428. (37) Balucani, N.; Skouteris, D.; Leonori, F.; Petrucci, R.; Hamberg, M.; Geppert, W. D.; Casavecchia, P.; Rosi, M. Combined Crossed Beam and Theoretical Studies of the N(2D) + CH4 Reaction and Implications for Atmospheric Models of Titan. J. Phys. Chem. A 2009, 113 (42), 11138−11152. (38) Balucani, N.; Skouteris, D.; Leonori, F.; Petrucci, R.; Hamberg, M.; Geppert, W. D.; Casavecchia, P.; Rosi, M. Combined Crossed Beam and Theoretical Studies of the N(2D) + C2H4 Reaction and Implications for Atmospheric Models of Titan. J. Phys. Chem. A 2012, 116 (43), 10467−10479. (39) Hasenkopf, C. A.; Beaver, M. R.; Trainer, M. G.; Dewitt, H. L.; Freedman, M. A.; Toon, O. B.; McKay, C. P.; Tolbert, M. A. Optical Properties of Titan and Early Earth Haze Laboratory Analogs in the Mid-Visible. Icarus 2010, 207 (2), 903−913. (40) Junninen, H.; Ehn, M.; Petäjä, T.; Luosujärvi, L.; Kotiaho, T.; Kostiainen, R.; Rohner, U.; Gonin, M.; Fuhrer, K.; Kulmala, M.; et al. A High-Resolution Mass Spectrometer to Measure Atmospheric Ion Composition. Atmos. Meas. Tech. 2010, 3 (4), 1039−1053. (41) DeCarlo, P. F.; Kimmel, J. R.; Trimborn, A.; Northway, M. J.; Jayne, J. T.; Aiken, A. C.; Gonin, M.; Fuhrer, K.; Horvath, T.; Docherty, K. S.; et al. Field-Deployable, High-Resolution, Time-ofFlight Aerosol Mass Spectrometer. Anal. Chem. 2006, 78 (24), 8281− 8289. (42) Stark, H.; Yatavelli, R. L. N.; Thompson, S. L.; Kimmel, J. R.; Cubison, M. J.; Chhabra, P. S.; Canagaratna, M. R.; Jayne, J. T.; Worsnop, D. R.; Jimenez, J. L. Methods to Extract Molecular and Bulk Chemical Information from Series of Complex Mass Spectra with Limited Mass Resolution. Int. J. Mass Spectrom. 2015, 389, 26−38. (43) Cubison, M. J.; Jimenez, J. L. Statistical Precision of the Intensities Retrieved from Constrained Fitting of Overlapping Peaks in High-Resolution Mass Spectra. Atmos. Meas. Tech. 2015, 8 (6), 2333−2345. (44) Heinritzi, M.; Simon, M.; Steiner, G.; Wagner, A. C.; Kürten, A.; Hansel, A.; Curtius, J. Characterization of the Mass-Dependent Transmission Efficiency of a CIMS. Atmos. Meas. Tech. 2016, 9 (4), 1449−1460. I


Article

ACS Earth and Space Chemistry (45) Hörst, S. M.; Tolbert, M. A. In Situ Measurements of the Size and Density of Titan Aerosol Analogs. Astrophys. J., Lett. 2013, 770 (1), 1−6. (46) Hörst, S. M.; Tolbert, M. A. The Effect of Carbon Monoxide on Planetary Haze Formation. Astrophys. J. 2014, 781 (1), 53−58. (47) Tammet, H.; Hõrrak, U.; Laakso, L.; Kulmala, M. Factors of Air Ion Balance in a Coniferous Forest According to Measurements in Hyytiälä, Finland. Atmos. Chem. Phys. 2006, 6 (11), 3377−3390. (48) Wilson, E. H.; Atreya, S. K. Current State of Modeling the Photochemistry of Titan’s Mutually Dependent Atmosphere and Ionosphere. J. Geophys. Res. 2004, 109 (E6), 1−39. (49) Lebonnois, S.; Bakes, E. L. O.; McKay, C. P. Transition from Gaseous Compounds to Aerosols in Titan’s Atmosphere. Icarus 2002, 159 (2), 505−517. (50) Coustenis, A.; Achterberg, R. K.; Conrath, B. J.; Jennings, D. E.; Marten, A.; Gautier, D.; Nixon, C. A.; Flasar, F. M.; Teanby, N. A.; Bézard, B.; et al. The Composition of Titan’s Stratosphere from Cassini/CIRS Mid-Infrared Spectra. Icarus 2007, 189 (1), 35−62. (51) Hunter, E. P.; Lias, S. G. Evaluated Gas-Phase Basicities and Proton Affinities of Molecules: An Update. J. Phys. Chem. Ref. Data 1998, 27 (3), 413−656. (52) Vuitton, V.; Bonnet, J.-Y.; Frisari, M.; Thissen, R.; Quirico, E.; Dutuit, O.; Schmitt, B.; Le Roy, L.; Fray, N.; Cottin, H.; et al. Very High Resolution Mass Spectrometry of HCN Polymers and Tholins. Faraday Discuss. 2010, 147, 495−508. (53) Somogyi, A.; Oh, C. H.; Smith, M. A.; Lunine, J. I. Organic Environments on Saturn’s Moon, Titan: Simulating Chemical Reactions and Analyzing Products by FT-ICR and Ion-Rrap Mass Spectrometry. J. Am. Soc. Mass Spectrom. 2005, 16 (6), 850−859. (54) Neish, C. D.; Somogyi, Á .; Imanaka, H.; Lunine, J. I.; Smith, M. A. Rate Measurements of the Hydrolysis of Complex Organic Macromolecules in Cold Aqueous Solutions: Implications for Prebiotic Chemistry on the Early Earth and Titan. Astrobiology 2008, 8 (2), 273−287. (55) Gautier, T.; Carrasco, N.; Schmitz-Afonso, I.; Touboul, D.; Szopa, C.; Buch, A.; Pernot, P. Nitrogen Incorporation in Titan’s Tholins Inferred by High Resolution Orbitrap Mass Spectrometry and Gas Chromatography-Mass Spectrometry. Earth Planet. Sci. Lett. 2014, 404, 33−42. (56) Gautier, T.; Carrasco, N.; Buch, A.; Szopa, C.; SciammaO’Brien, E.; Cernogora, G. Nitrile Gas Chemistry in Titan’s Atmosphere. Icarus 2011, 213 (2), 625−635. (57) Carslaw, K. S.; Harrison, R. G.; Kirkby, J. Cosmic Rays, Cloods and Climate. Science 2002, 298 (5599), 1732−1737. (58) Jackman, C. H.; Marsh, D. R.; Kinnison, D. E.; Mertens, C. J.; Fleming, E. L. Atmospheric Changes Caused by Galactic Cosmic Rays over the Period 1960−2010. Atmos. Chem. Phys. 2016, 16 (9), 5853− 5866. (59) Mutsukura, N. Deposition of Diamondlike Carbon Film and Mass Spectrometry Measurement in CH 4/N 2 RF Plasma. Plasma Chem. Plasma Process. 2001, 21 (2), 265−277. (60) Thissen, R.; Vuitton, V.; Lavvas, P.; Lemaire, J.; Dehon, C.; Dutuit, O.; Smith, M. A.; Turchini, S.; Catone, D.; Yelle, R. V.; et al. Laboratory Studies of Molecular Growth in the Titan Ionosphere. J. Phys. Chem. A 2009, 113 (42), 11211−11220. (61) Sagan, C.; Khare, B. N. Tholins: Organic Chemistry of Interstellar Grains and Gas. Nature 1979, 277 (5692), 102−107. (62) Holtz, D.; Beauchamp, J. L. Nitrogen and Carbon Monoxide as Nucleophilic Reagents in Gas Phase Displacement Reactions: A Novel Means of Nitrogen Fixation. Nature, Phys. Sci. 1971, 231, 204− 205. (63) Waite, J. H.; Niemann, H.; Yelle, R. V.; Kasprzak, W. T.; Cravens, T. E.; Luhmann, J. G.; McNutt, R. L.; Ip, W. H.; Gell, D.; De La Haye, V.; et al. Ion Neutral Mass Spectrometer Results from the First Flyby of Titan. Science 2005, 308 (5724), 982−986. (64) Mandt, K. E.; Gell, D. A.; Perry, M.; Hunter Waite, J.; Crary, F. A.; Young, D.; Magee, B. A.; Westlake, J. H.; Cravens, T.; Kasprzak, W.; et al. Ion Densities and Composition of Titan’s Upper Atmosphere Derived from the Cassini Ion Neutral Mass Spectrom-

eter: Analysis Methods and Comparison of Measured Ion Densities to Photochemical Model Simulations. J. Geophys. Res. E Planets 2012, 117 (10), 1−22. (65) Cravens, T. E.; Yelle, R. V.; Wahlund, J.-E.; Shemansky, D. E.; Nagy, A. F. Composition and Structure of the Ionosphere and Thermosphere. In Titan from Cassini-Huygens; Springer: Dordrecht, 2009; pp 259−296. (66) Lavvas, P. P.; Coustenis, A.; Vardavas, I. M. Coupling Photochemistry with Haze Formation in Titan’s Atmosphere, Part II: Results and Validation with Cassini/Huygens Data. Planet. Space Sci. 2008, 56 (1), 67−99. (67) Crary, F. J.; Magee, B. A.; Mandt, K.; Waite, J. H.; Westlake, J.; Young, D. T. Heavy Ions, Temperatures and Winds in Titan’s Ionosphere: Combined Cassini CAPS and INMS Observations. Planet. Space Sci. 2009, 57 (14−15), 1847−1856. (68) Sebree, J. A.; Trainer, M. G.; Loeffler, M. J.; Anderson, C. M. Titan Aerosol Analog Absorption Features Produced from Aromatics in the Far Infrared. Icarus 2014, 236, 146−152. (69) Milligan, D. B.; Freeman, C. G.; Maclagan, R. G. A. R.; McEwan, M. J.; Wilson, P. F. Termolecular Ion−Molecule Reactions in Titan’s Atmosphere. II: The Structure of the Association Adducts of HCNH+ With C2H2 and C2H4. J. Am. Soc. Mass Spectrom. 2001, 12 (5), 557−564. (70) Dobrijevic, M.; Loison, J. C.; Hickson, K. M.; Gronoff, G. 1DCoupled Photochemical Model of Neutrals, Cations and Anions in the Atmosphere of Titan. Icarus 2016, 268, 313−339. (71) Hicks, R. K. Mechanistic Studies of Planetary Haze Formation, Ph.D. Thesis, University of Colorado, Boulder, CO, 2015. (72) Imanaka, H.; Khare, B. N.; Elsila, J. E.; Bakes, E. L. O.; McKay, C. P.; Cruikshank, D. P.; Sugita, S.; Matsui, T.; Zare, R. N. Laboratory Experiments of Titan Tholin Formed in Cold Plasma at Various Pressures: Implications for Nitrogen-Containing Polycyclic Aromatic Compounds in Titan Haze. Icarus 2004, 168 (2), 344−366. (73) Reid Thompson, W.; Henry, T. J.; Schwartz, J. M.; Khare, B. N.; Sagan, C. Plasma Discharge in N2+ CH4at Low Pressures: Experimental Results and Applications to Titan. Icarus 1991, 90 (1), 57−73. (74) Flasar, F. M.; Achterberg, R. K.; Conrath, B. J.; Gierasch, P. J.; Kunde, V. G.; Nixon, C. A.; Bjoraker, G. L. Titan’s Atmospheric Temperatures, Winds, and Composition. Observatory 2009, 975 (2005), 975−979. (75) Fulchignoni, M.; Ferri, F.; Angrilli, F.; Ball, A. J.; Bar-Nun, A.; Barucci, M. A.; Bettanini, C.; Bianchini, G.; Borucki, W.; Colombatti, G.; et al. In Situ Measurements of the Physical Characteristics of Titan’s Environment. Nature 2005, 438 (7069), 785−791. (76) Grard, R.; Hamelin, M.; López-Moreno, J. J.; Schwingenschuh, K.; Jernej, I.; Molina-Cuberos, G. J.; Simões, F.; Trautner, R.; Falkner, P.; Ferri, F.; et al. Electric Properties and Related Physical Characteristics of the Atmosphere and Surface of Titan. Planet. Space Sci. 2006, 54 (12), 1124−1136. (77) Molina-Cuberos, G. J.; López-Moreno, J. J.; Rodrigo, R.; Lara, L. M. Chemistry of the Galactic Cosmic Ray Induced Ionosphere of Titan. J. Geophys. Res. Planets 1999, 104 (E9), 21997−22024. (78) Molina-Cuberos, G. J.; Schwingenschuh, K.; López-Moreno, J. J.; Rodrigo, R.; Lara, L. M.; Anicich, V. Nitriles Produced by Ion Chemistry in the Lower Ionosphere of Titan. J. Geophys. Res. Planets 2002, 107 (E11), 9−11. (79) Molina-Cuberos, G. J.; López-Moreno, J. J.; Rodrigo, R.; Lara, L. M.; O’Brien, K. Ionization by Cosmic Rays of the Atmosphere of Titan. Planet. Space Sci. 1999, 47 (10−11), 1347−1354. (80) Vuitton, V.; Yelle, R. V.; Klippenstein, S. J.; Hörst, S. M.; Lavvas, P. Simulating the Density of Organic Species in the Atmosphere of Titan with a Coupled Ion-Neutral Photochemical Model. Icarus 2018, DOI: 10.1016/j.icarus.2018.06.013. (81) Loison, J. C.; Hébrard, E.; Dobrijevic, M.; Hickson, K. M.; Caralp, F.; Hue, V.; Gronoff, G.; Venot, O.; Bénilan, Y. The Neutral Photochemistry of Nitriles, Amines and Imines in the Atmosphere of Titan. Icarus 2015, 247, 218−247.

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