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1.
Abstract— The polycyclic aromatic hydrocarbon (PAH) naphthalene was exposed to ultraviolet radiation in H2O ice under astrophysical conditions, and the products were analyzed using infrared spectroscopy and high‐performance liquid chromatography. As we found in our earlier studies on the photoprocessing of coronene in H2O ice, aromatic alcohols and ketones (quinones) were formed. The regiochemistry of the reactions is described and leads to specific predictions of the relative abundances of various oxidized naphthalenes that should exist in meteorites if interstellar ice photochemistry influenced their aromatic inventory. Since oxidized PAHs are present in carbon‐rich meteorites and interplanetary dust particles (IDPs), and ubiquitous in and fundamental to biochemistry, the delivery of such extraterrestrial molecules to the early Earth may have played a role in the origin and evolution of life.  相似文献   

2.
Observations of cometary comae in the infrared and in the near-ultraviolet suggest that polycyclic aromatic hydrocarbons (PAHs) are present in these environments. However, the chemical identity and abundance of these molecules are not clearly determined yet. Some species are probably more stable than others when submitted to the solar radiation field, and are therefore more likely to be observed. The photophysics of gas-phase PAHs in cometary environments is modelled. Photodissociation occurs when the heating by absorption of UV photons is more efficient than the radiative cooling. The lifetime of the molecules is found to depend on their size: small molecules being more stable than large ones. Furthermore, at 1 AU from the Sun, the lifetime of PAHs is found to be very short (20s for phenanthrene). This suggests that, if observed in the gas phase in cometary environments, these molecules should be produced by an extended source.  相似文献   

3.
Abstract– Even in the absence of any biosphere on Mars, organic molecules, including polycyclic aromatic hydrocarbons (PAHs), are expected on its surface due to delivery by comets and meteorites of extraterrestrial organics synthesized by astrochemistry, or perhaps in situ synthesis in ancient prebiotic chemistry. Any organic compounds exposed to the unfiltered solar ultraviolet spectrum or oxidizing surface conditions would have been readily destroyed, but discoverable caches of Martian organics may remain shielded in the subsurface or within surface rocks. We have studied the stability of three representative polycyclic aromatic hydrocarbons (PAHs) in a Mars chamber, emulating the ultraviolet spectrum of unfiltered sunlight under temperature and pressure conditions of the Martian surface. Fluorescence spectroscopy is used as a sensitive indicator of remaining PAH concentration for laboratory quantification of molecular degradation rates once exposed on the Martian surface. Fluorescence‐based instrumentation has also been proposed as an effective surveying method for prebiotic organics on the Martian surface. We find the representative PAHs, anthracene, pyrene, and perylene, to have persistence half‐lives once exposed on the Martian surface of between 25 and 60 h of noontime summer UV irradiation, as measured by fluorescence at their peak excitation wavelength. This equates to between 4 and 9.6 sols when the diurnal cycle of UV light intensity on the Martian surface is taken into account, giving a substantial window of opportunity for detection of organic fluorescence before photodegradation. This study thus supports the use of fluorescence‐based instrumentation for surveying recently exposed material (such as from cores or drill tailings) for native Martian organic molecules in rover missions.  相似文献   

4.
We studied the stability of aromatic compounds in low Earth orbit environment and describe the scientific results and successful flight of the ORGANICS experiment on-board the BIOPAN V space exposure facility. This experiment investigated the photo stability of large organic molecules in low Earth orbit. Thin films of selected organic molecules, such as polycyclic aromatic hydrocarbons (PAHs) and the fullerene C60 were subjected to the low Earth orbit environment and the samples were monitored before and after flight. PAHs and fullerenes have been proposed as carriers for a number of astronomical absorption and emission features and are also identified in meteorites. Our experiment on BIOPAN V was exposed to a total fluence of 602.45 kJ m−2 for photons in the range 170–280 nm. The experiment was also intended as a hardware test-flight for a long-term exposure experiment (Survival of organics in space) on the EXPOSE facility on the International Space Station (ISS). For the small fluence that was collected during the BIOPAN V experiment we found little evidence of photo-destruction. The results confirm that PAH molecules are very stable compounds in space. The small differences in destruction rates that are expected to arise among the PAH samples as a function of molecular size and structure will only show after the longer irradiation fluences that are expected in the exposure experiment on the ISS.  相似文献   

5.
Abstract— We report on the molecular analyses of the water‐ and solvent‐soluble organic compounds released from the insoluble organic material (IOM) of the Murray meteorite upon treatment with weight‐equivalent amounts of water and under conditions of elevated temperature and pressure. A varied suite of compounds was identified by gas chromatography‐mass spectrometry (GC‐MS). C3‐C17 alkyl dicarboxylic acids and N‐ and O‐containing hydroaromatic and aromatic compounds were found in the water extracts. The solvent extracts contained N‐, O‐, and S‐containing aromatic compounds, a large number of their isomers and homologs, and a series of polycyclic aromatic hydrocarbons (PAHs) of up to five rings, together with noncondensed aromatic species such as substituted benzenes, biphenyl, and terphenyls as well as their substituted homologs, and hydrated PAHs. Isotopic analyses showed that residue IOMs after hydrothermal treatment had lower deuterium and 15N content than the untreated material (ΔD = ?833‰ and Δ15N = ?24.1) but did not differ from it in 13C composition. The effect of the hydrothermolytic release was recorded in significant differences between the NMR spectra of untreated and residue IOM. A possible relation to common precursors for the dicarboxylic acids found in the IOM and bulk extracts is discussed.  相似文献   

6.
We have developed antibodies and a multi-array competitive immunoassay (MACIA) for the detection of a wide range of molecular size compounds, from single aromatic ring derivatives or polycyclic aromatic hydrocarbons (PAHs), through small peptides, proteins or whole cells (spores). Multiple microarrays containing target molecules are used simultaneously to run several competitive immunoassays. The sensitivity of the MACIA for small organic compounds like naphthalene, 4-phenilphenol or 4-tertbutilphenol is in the range of 100–500 ppb (ng ml−1), for others like the insecticide terbutryn it is at the ppt (ng l−1) level, while for small peptides, as well as for more complex molecules like the protein thioredoxin, the sensitivity is approximately 1–2 ppb, or 104–105 spores of Bacillus subtilis per milliliter. For organic compounds, a water–methanol solution was used in order to achieve a better dissolution of the organics without compromising the antibody–antigen interaction. The above-mentioned compounds were detected by MACIA in water–(10%) methanol extracts from spiked pyrite and hematite-containing rock powder samples, as well as from a spiked-sand sample subjected to organic extraction with dichloromethane–methanol (1/1).  相似文献   

7.
Radiation synthesis has been proposed as a mechanism for changing the nature of the outer few meters of ice in a comet stored 4.6 billion years in the Oort cloud and may explain some of the differences observed between new and more evolved comets. Cometary-type ice mixtures were studied in a laboratory experiment designed to approximately simulate the expected temperature, pressure, and radiation environment of the interstellar Oort cloud region. The 2.5- to 15-μm infrared absorption features of thin ice films were analyzed near 20°K before and after 1 MeV proton irradiation. Various ice mixtures included the molecules H2O, NH3, CH4, N2, C3H8, CO, and CO2. All experiments confirm the synthesis of new molecular species in solid phase mixtures at 20°K. The synthesized molecules, identified by their infrared signatures, are C2H6, CO2, CO, N2O, NO, and CH4 (weak). Synthesized molecules, identified by gas chromatographic (GC) analysis of the volatile fraction of the warmed irradiated ice mixture, are C2H4 or C2H6, and C3H8. When CH4 is present in the irradiated ice mixture, long-chained volatile hydrocarbons and CO2 are synthesized along with high-molecular-weight carbon compounds present in the room temperature residue. Irradiated mixtures containing CO and H2O synthesize CO2 and those CO2 and H2O synthesize CO. Due to radiation synthesis, ～1% of the ice was converted into a nonvolatile residue containing complicated carbon compounds not present in blank samples. These results suggest that irrespective of the composition of newly accreted comets, initial molecular abundances can be altered and new species created as a result of radiation synthesis. Irradiated mixtures exhibited thermoluminescence and pressure enhancements during warming; these phenomena suggest irradiation synthesis of reactive species. Ourbursts in new comets resulting from similar radiation induced exothermic activity would be expected to occur beginning at distances of the order of 100 AU.  相似文献   

8.
Aromatic hydrocarbons account for a significant portion of the organic matter in carbonaceous chondrite meteorites, as a component of both the low molecular weight, solvent-extractable compounds and the insoluble organic macromolecular material. Previous work has suggested that the aromatic compounds in carbonaceous chondrites may have originated in the radiation-processed icy mantles of interstellar dust grains. Here we report new studies of the organic residue made from benzene irradiated at 19 K by 0.8 MeV protons. Polyphenyls with up to four rings were unambiguously identified in the residue by gas chromatography–mass spectrometry. Atmospheric pressure photoionization Fourier transform mass spectrometry was used to determine molecular composition, and accurate mass measurements suggested the presence of polyphenyls, partially hydrogenated polyphenyls, and other complex aromatic compounds. The profile of low molecular weight compounds in the residue compared well with extracts from the Murchison and Orgueil meteorites. These results are consistent with the possibility that solid phase radiation chemistry of benzene produced some of the complex aromatics found in meteorites.  相似文献   

9.
A mixture of the polycyclic aromatic hydrocarbons (PAHs), acenaphthylene and acenaphthene, when subjected to the energetic environment of a hydrogen plasma, is transformed into a material that exhibits an infrared absorption profile in the 3 micron region that is an excellent match of the protoplanetary nebula IRAS 05341+0852 emission profile in the same wavelength region. Acenaphthylene and acenaphthene were chosen as precursors in the experiment because these molecules have a structure that can be described as a keystone in a process in which carbon atoms in a stellar wind condense into PAH species. The spectral match between experiment and observations appears to validate that scenario.  相似文献   

10.
The observations of dust gas in diffuse and molecular clouds are shown to reflect not only their current state but their past history. The interpretation of infrared spectra of dust in molecular clouds using appropriate core-mantle grains shows that: (1) the kinds and amounts of ices, (2) the relative proportion of such important interstellar molecules as H2O and CO, (3) the evidence for the less abundant solid species X–CN, COS, H2S, and (4) the thermal history of the dust may all be demonstrated quantitatively from laboratory analog studies of ultraviolet photoprocessing of relevant ices and from theoretical studies of gas-dust interactions. In diffuse clouds the dust is shown to consist predominantly of refractory organic compounds which originate as residues of the photoprocessing of volatile ices in molecular clouds and which undergo further physical and chemical evolution in the diffuse clouds.Review paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986.  相似文献   

11.
Haze particles exert a significant influence over the thermodynamics and radiation absorption properties of the Titan haze, as well as its complex organic chemistry. Characterization of both the molecular and the submicrometer components of the haze is therefore vital for understanding the global properties of Titan. We have carried out a Titan tholin synthesis experiment and measured the time variation of the infrared spectrum of the product as a thin film developed. Also, to examine the possibility of oxygen contamination, we compared the infrared spectrum of the tholin film with that of a tholin film exposed to dry air and laboratory air. The objective of this study is to understand the chemical processes related to how simple organic molecules are processed into more complex haze particles. The progressive development of features characteristic of amines, aromatic and aliphatic hydrocarbons, and nitriles in the experimental mixture is clear. Of particular interest is the formation of aromatic rings after only a few seconds of glow discharge, indicating that these compounds appear to be intermediates between simple haze molecules and microphysical aerosols. The early dominance of aromatic ring structures is accompanied during the later stages of the experiment by the appearance of nitrile and amine compounds. This time-dependent succession of chemical structures provides vital clues to the possible chemical formation pathways of Titan haze aerosols.  相似文献   

12.
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13.
Large polycyclic aromatic hydrocarbons (PAHs) are an important component of the interstellar medium. PAHs have been identified in the soluble and insoluble matter of carbonaceous chondrites (CCs). Here, we study the evolution of PAHs under conditions relevant to the interiors of asteroids and compare our results to PAHs observed in CCs. We have performed long‐term and short‐term hydrothermal experiments, in which we exposed PAH‐mineral mixture analogs of meteorites to temperature conditions representative of those predicted for asteroids interiors. Our results show that small PAHs with melting points within the aqueous alteration temperature of CCs form carbonaceous spherules in the presence of water. In this work, we describe the microstructure and morphology of these spherules. We discuss the similarities and differences compared to globules isolated from CCs.  相似文献   

14.
A detailed study is made on the variation of the 12 μm emission of the H-II region-molecular cloud complex S 252 with the radiation field, using the IRAS data. The results show that, in order to explain the excess short wave emission, we must consider non-equilibrium emission by very small dust particles (PAHs and other small particles). These small grains emit 36% of the total infrared luminosity, mostly in the range shorter than 25 μm. The PAHs are severely depleted by the radiation field in the H-II region; in the dense cloud, they are less so because of the shielding by the cloud. A model incorporating a radial distribution of PAHs in the H-II region can satisfactorily explain the observed spatial variation of the 12 μm emission.  相似文献   

15.
Unidentified infrared emission bands (UIR bands) have been attributed to polycyclic aromatic hydrocarbons (PAHs), which are believed to require ultraviolet radiation in order for the UIR bands to be excited. If, in addition to amorphous carbon and hydrogenated amorphous carbon (HAC) particles, PAHs are able to form in the outflows of cool carbon-rich stars (Cherchneff et al. 1991), then the weak UV radiation field from such stars would be unlikely to be able to excite the UIR bands and so the PAH species could remain undetected in the spectra of C-stars. However, cool carbon stars with hot companions might be exposed to strong enough UV radiation fields for UIR-band emission to be excited from PAHs. Buss et al. (1991) reported the detection of the 8 μm UIR-band (C-C stretch) in the IRAS LRS spectrum of HD 38218 (TU Tau), a carbon star with a hotter A2III companion. To investigate the phenomenon further, we have therefore obtained UKIRT CGS3 10 μm spectra of three carbon stars with hot companions, TU Tau, UV Aur and CS776. It was found that TU Tau showed the 11.25 μm and 8.6 μm UIR-bands (both attributed to C-H bend modes) at good contrast, while UV Aur clearly exhibited the 11.25 μm UIR band. No narrow UIR-band emission was detected in the spectrum of CS776. We have fitted these 10 μm region spectra using a χ2-minimization program equipped to fit stellar and dust emission continua together with the broad SiC feature and the narrow UIR-bands. The features seen in the spectra of TU Tau and UV Aur can be well fitted by a narrow 11.25 μm UIR-band sitting on top of a broad, self-absorbed 11.3 μm silicon carbide feature. Our results therefore provide strong support for the supposition that PAHs can form in carbon star outflows. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

16.
The nature of unidentified cometary emission lines is discussed. A model of ice particles in cometary halos as a mixture of frozen polycyclic aromatic hydrocarbons (PAHs) and acyclic hydrocarbons is considered. The properties of frozen hydrocarbon particles are described and 5–7% of the unidentified cometary emission lines are considered as the photoluminescence of frozen hydrocarbons. The positions of unidentified emission lines in the spectrum of Comet 19P/Borrelly are compared with the positions of quasi-lines in the photoluminescence spectra of PAHs that were dissolved in acyclic hydrocarbons at a temperature of 77 K and that constitute a polycrystalline solution.  相似文献   

17.
The Space Environment Viability of Organics (SEVO) experiment is one of two scientific payloads aboard the triple-cube satellite Organism/ORganic Exposure to Orbital Stresses (O/OREOS). O/OREOS is the first technology demonstration mission of the NASA Astrobiology Small Payloads Program. The 1-kg, 1000-cm3 SEVO cube is investigating the chemical evolution of organic materials in interstellar space and planetary environments by exposing organic molecules under controlled conditions directly to the low-Earth orbit (LEO) particle and electromagnetic radiation environment. O/OREOS was launched on November 19, 2010 into a 650-km, 72°-inclination orbit and has a nominal operational lifetime of six months. Four classes of organic compounds, namely an amino acid, a quinone, a polycyclic aromatic hydrocarbon (PAH), and a metallo-porphyrin are being studied. Initial reaction conditions were established by hermetically sealing the thin-film organic samples in self-contained micro-environments. Chemical changes in the samples caused by direct exposure to LEO radiation and by interactions with the irradiated microenvironments are monitored in situ by ultraviolet/visible/near-infrared (UV/VIS/NIR) absorption spectroscopy using a novel compact fixed-grating CCD spectrometer with the Sun as its light source. The goals of the O/OREOS mission include: (1) demonstrating key small satellite technologies that can enable future low-cost astrobiology experiments, (2) deploying a miniature UV/VIS/NIR spectrometer suitable for in-situ astrobiology and other scientific investigations, (3) testing the capability to establish a variety of experimental reaction conditions to enable the study of astrobiological processes on small satellites, and (4) measuring the chemical evolution of organic molecules in LEO under conditions that can be extrapolated to interstellar and planetary environments. In this paper, the science and technology development of the SEVO instrument payload and its measurements are described.  相似文献   

18.
Polycyclic aromatic hydrocarbons (PAHs) are important components of the interstellar medium and carbonaceous chondrites, but have never been identified in the reducing atmospheres of the outer solar system. Incompletely characterized complex organic solids (tholins) produced by irradiating simulated Titan atmospheres reproduce well the observed UV/visible/IR optical constants of the Titan stratospheric haze. Titan tholin and a tholin generated in a crude simulation of the atmosphere of Jupiter are examined by two-step laser desorption/multiphoton ionization mass spectrometry. A range of two- to four-ring PAHs, some with one to four alkylation sites are identified, with net abundance approximately 10(-4) g g-1 (grams per gram) of tholins produced. Synchronous fluorescence techniques confirm this detection. Titan tholins have proportionately more one- and two-ring PAHs than do Jupiter tholins, which in turn have more four-ring and larger PAHs. The four-ringed PAH chrysene, prominent in some discussions of interstellar grains, is found in Jupiter tholins. Solid state 13C NMR spectroscopy suggests approximately equal to 25% of the total C in both tholins is tied up in aromatic and/or aliphatic alkenes. IR spectra indicate an upper limit in both tholins of approximately equal to 6% by mass in benzenes, heterocyclics, and PAHs with more than four rings. Condensed PAHs may contribute at most approximately 10% to the observed detached limb haze layers on Titan. As with interstellar PAHs, the synthesis route of planetary PAHs is likely to be via acetylene addition reactions.  相似文献   

19.
The photolysis of nitrous oxide has been studied in a flow system using xenon resonance radiation at 1470 and 1295 Å and krypton resonance radiation at 1236 and 1165 Å. The average quantum yields with regard to decomposed nitrous oxide, nitrogen and higher oxides of nitrogen were found to be larger in the experiments using the longer wave lengths than in the experiments using the 1236 and 1165 Å radiation. The ratio of the quantum yield with respect to oxygen and nitrogen was found to be lower in the experiments with the resonance radiation of xenon than in the experiments with the resonance radiation of krypton.

From the data obtained, it can be assumed that at the xenon resonance radiation the initial absorption of a light quantum leads to the production of nitrogen molecules and oxygen atoms. At the shorter wave lengths, the initial absorption act probably proceeds in a dual manner. It is supposed that both the splitting of nitrous oxide into nitrogen molecules and oxygen atoms and into nitrogen atoms and nitric oxide occurs at this radiation.  相似文献   


20.
In the interstellar medium, the most probable source of organic molecules could be non-equilibrium processes driven by photons, cosmic rays, shock waves and solid bodies’ collisions. The dense cold phase of ISM host icy dust grains—important chemical catalyst during its life cycle. Such particles consist of mineral core composed by silicate or olivine admixed with metal sulfides and oxides, with the water-icy envelope containing organic molecules. Organic molecules in the ISM evolve and become later incorporated in solar system material (comets and meteorites).The formation of polypeptides from single amino acids was traced in simulation experiments representing the inner structure of icy dust grains. Experimental chamber was irradiated at subzero temperatures at the dosage of 2.54 kRad/min. Solid frozen solutions of Gly and Phe were taken as the experimental samples inserted into the metal tube kept at subzero temperatures in the presence of liquid nitrogen. Formation of di- and tri-peptides was demonstrated after applying mass-spectrometry and high performance liquid chromatography (HPLC) techniques.Having polypeptides within the icy matrix, dust grains with ice mantles are transported to warm, dense and active protostellar regions, where ultraviolet irradiation may become important and alter the grain composition. Furthermore UVC radiation may contribute to the formation of additional amounts of polypeptides, since short-wave photons are totally adsorbed by a thin outer layer. This presumption coincides with our previous investigations concerning UV impact on prebiotic formation of the main biological molecules. Combination of two irradiation types in different stages of interstellar flight could compensate the effects of low reagents concentration and temperature. Since the primordial Earth had no atmosphere, the natural carriers could get freely onto its surface and thus raise the concentration of organic molecules.  相似文献   

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