Infrared spectra and optical constants of astronomical ices: IV. Benzene and pyridine

Hudson, R. L.; Yarnall, Yukiko Y.

doi:10.1016/j.icarus.2022.114899

Cited by 19 publications

(11 citation statements)

References 42 publications

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“…Here, the theoretical spectrum aligns with experiment where the ν 12 , ν 13 , ν 14 , and ν 4 modes are the most intense bands of ungerade symmetry, while the ν 5 , ν 9 , ν 10 , ν 6 , and ν 19 modes are comparatively weak (Table S1). The C 6 H 6 crystal (space group Pbca , Z = 4) is relevant to planetary (i.e., Titan) and interstellar environments and has therefore been previously characterized by IR spectroscopy in this context, , in addition to fundamental studies on both liquid and gas-phase benzene. , Various notations for labeling the vibrational modes of C 6 H 6 prevail, of which Herzberg notation is used in this work . Despite its high molecular symmetry, the experimental spectrum recorded after deposition at 15 K displays many peaks attributed to a more disordered amorphous phase, which are compiled in Table S1.…”

Section: Resultsmentioning

confidence: 99%

“…This resulted in thin films of ca. 1–5 μm thickness as calculated by the integration of IR band profiles and applying literature band strengths (A′) for crystalline C 2 H 2 (ν 5 : 22.2 × 10 –18 cm molecule –1 ) and crystalline C 6 H 6 (ν 4 : 15.5 × 10 –18 cm molecule –1 ) , that have been compiled under similar chamber conditions using a transmission IR geometry. Mid-IR spectra (500–4000 cm –1 ) were collected with a benchtop FTIR spectrometer (Thermo iG50) with an internal Globar (SiC) thermal light source, and a liquid-N 2 cooled midband mercury–cadmium–telluride (MCT-B) detector.…”

Section: Methodsmentioning

confidence: 99%

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Simulation of Cocrystal Formation in Planetary Atmospheres: The C₆H₆:C₂H₂ Cocrystal Produced by Gas Deposition

et al. 2023

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The formation of molecular cocrystals in condensed aerosol particles has been recently proposed as an efficient pathway for generation of complex organics in Titan's atmosphere. It follows that cocrystal precipitation may facilitate the transport of biologically important precursors to the surface to be sequestered in an organic karstic and sand environment. Recent laboratory studies on these planetary minerals have predominantly synthesized cocrystals by the controlled freezing of binary mixtures from the liquid phase, allowing for their structural and spectroscopic characterization. However, these techniques are perhaps not best representative of aerosol nucleation and growth microphysics in planetary atmospheres. Herein, we report the first synthesis of the known 1:1 C 6 H 6 :C 2 H 2 cocrystal using vapor deposition methods onto a cryogenically cooled substrate. Subsequent transmission FTIR spectroscopy has confirmed the formation of the empirical C 6 H 6 :C 2 H 2 cocrystal structure via the observation of diagnostic infrared spectral features. Predicted by periodic-DFT calculations, altered vibrational profiles depict a changing site symmetry of the C 6 H 6 and C 2 H 2 components after transition to the cocrystal unit cell geometry. The 80 K temperature of the cocrystal phase transition overlaps with the condensation curves obtained for both species in Titan's lower stratosphere, revealing that the cocrystal may act as an important environment for photo-and radio-lytic processes leading to the formation of higher order organics in Titan's atmosphere. Such solid-state astrochemistry can now be pursued in oxygen-free laboratory settings under (ultra)high vacuum using standard surface science setups.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Simulation of Cocrystal Formation in Planetary Atmospheres: The C₆H₆:C₂H₂ Cocrystal Produced by Gas Deposition

et al. 2023

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“…The B value of C 6 H 6 was obtained from a previously reported value for pure solids (Szczepaniak & Person 1972). Although Hudson & Yarnall (2022) recently reported the absolute intensity of the 1477 cm −1 feature of benzene in an H 2 O-rich environment, pure solid values were used in the present study because the reported intensities are similar to each other within experimental error (∼10%), and the absolute intensities of several IR bands were required to estimate the column density as accurately as possible, especially its changes with H-atom irradiation. The B value of C 10 H 8 was adopted from a previously reported value for C 10 H 8 /H 2 O (1/15) ice (Sandford et al 2004).…”

Section: Methodsmentioning

confidence: 99%

Penetration of Nonenergetic Hydrogen Atoms into Amorphous Solid Water and their Reaction with Embedded Benzene and Naphthalene

Tsuge

Kouchi

Watanabe

2022

ApJ

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Chemical processes on the surface of icy grains play an important role in the chemical evolution in molecular clouds. In particular, reactions involving nonenergetic hydrogen atoms accreted from the gaseous phase have been extensively studied. These reactions are believed to effectively proceed only on the surface of the icy grains; thus, molecules embedded in the ice mantle are not considered to react with hydrogen atoms. Recently, Tsuge et al. suggested that nonenergetic hydrogen atoms can react with CO molecules even in ice mantles via diffusive hydrogenation. This investigation was extended to benzene and naphthalene molecules embedded in amorphous solid water (ASW) in the present study, which revealed that a portion of these molecules could be fully hydrogenated in astrophysical environments. The penetration depths of nonenergetic hydrogen atoms into porous and nonporous ASW were determined using benzene molecules to be >50 and ∼10 monolayers, respectively (1 monolayer ≈ 0.3 nm).

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“…Pyridine (C 5 H 5 N) is a simple nitrogen heterocycle, a class of molecules that have been identified in meteoritic organic matter, − and nitrogen-based heterocycles are fundamental to Earth-based life. , Additionally, the enhanced stability of aromatics, including pyridine, makes them good candidates for detection by both in situ and sample return missions . Although pyridine has not been directly detected in Titan’s atmosphere, when in the presence of HCN (which has been detected and routinely observed in Titan’s atmosphere − ), acetylene polymerization may produce N -heterocycles including pyridine. , Further, a ring expansion reaction (gas phase) between electron-deficient methyl carbyne (CH) and pyrrole (C 4 H 5 N) (an N -heterocycle) directly produces pyridine .…”

Section: Introductionmentioning

confidence: 99%

Experimental Characterization of the Pyridine:Acetylene Co-crystal and Implications for Titan’s Surface

Czaplinski

Cable

et al. 2023

ACS Earth Space Chem.

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Titan, Saturn's largest moon, has a plethora of organic compounds in the atmosphere and on the surface that interact with each other. Cryominerals such as co-crystals may influence the geologic processes and chemical composition of Titan's surface, which in turn informs our understanding of how Titan may have evolved, how the surface is continuing to change, and the extent of Titan's habitability. Previous works have shown that a pyridine:acetylene (1:1) co-crystal forms under specific temperatures and experimental conditions; however, this has not yet been demonstrated under Titan-relevant conditions. Our work here demonstrates that the pyridine:acetylene co-crystal is stable from 90 K, Titan's average surface temperature, up to 180 K under an atmosphere of N 2 . In particular, the co-crystal forms via liquid− solid interactions within minutes upon mixing of the constituents at 150 K, as evidenced by distinct, new Raman bands and band shifts. X-ray diffraction (XRD) results indicate moderate anisotropic thermal expansion (about 0.5−1.1%) along the three principal axes between 90−150 K. Additionally, the co-crystal is detectable after being exposed to liquid ethane, implying stability in a residual ethane "wetting" scenario on Titan. These results suggest that the pyridine:acetylene co-crystal could form in specific geologic contexts on Titan that allow for warm environments in which liquid pyridine could persist, and as such, this cryomineral may preserve the evidence of impact, cryovolcanism, or subsurface transport in surface materials.

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Infrared spectra and optical constants of astronomical ices: IV. Benzene and pyridine

Cited by 19 publications

References 42 publications

Simulation of Cocrystal Formation in Planetary Atmospheres: The C₆H₆:C₂H₂ Cocrystal Produced by Gas Deposition

Simulation of Cocrystal Formation in Planetary Atmospheres: The C₆H₆:C₂H₂ Cocrystal Produced by Gas Deposition

Penetration of Nonenergetic Hydrogen Atoms into Amorphous Solid Water and their Reaction with Embedded Benzene and Naphthalene

Experimental Characterization of the Pyridine:Acetylene Co-crystal and Implications for Titan’s Surface

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Infrared spectra and optical constants of astronomical ices: IV. Benzene and pyridine

Cited by 19 publications

References 42 publications

Simulation of Cocrystal Formation in Planetary Atmospheres: The C6H6:C2H2 Cocrystal Produced by Gas Deposition

Simulation of Cocrystal Formation in Planetary Atmospheres: The C6H6:C2H2 Cocrystal Produced by Gas Deposition

Penetration of Nonenergetic Hydrogen Atoms into Amorphous Solid Water and their Reaction with Embedded Benzene and Naphthalene

Experimental Characterization of the Pyridine:Acetylene Co-crystal and Implications for Titan’s Surface

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Simulation of Cocrystal Formation in Planetary Atmospheres: The C₆H₆:C₂H₂ Cocrystal Produced by Gas Deposition

Simulation of Cocrystal Formation in Planetary Atmospheres: The C₆H₆:C₂H₂ Cocrystal Produced by Gas Deposition