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Here, we present the results of the first solid-phase ex situ analysis of cosmic grain analogs produced at low temperature (<200 K) in the NASA Ames COsmic SImulation Chamber (COSmIC) from small hydrocarbon precursors, methane (CH4) and acetylene (C2H2), seeded in an argon supersonic jet expansion and submitted to a plasma discharge. The plasma-induced chemical reactions, initiated between the precursor molecules and their atomic and molecular fragments, radicals and ions, produce larger molecules and eventually solid particles that are collected in situ under controlled conditions. Scanning electron microscopy (SEM) imaging was used to provide insight on the morphology and growth structure of the grains produced in COSmIC, and to investigate how the precursors used to produce the grains affect these parameters. This SEM study has shown that under identical experimental conditions with fixed physical and chemical parameters (precursor density, temperature, energy, and reaction time), heavier precursors in the initial mixture produce larger grains and in larger quantity, most likely as a result of a more complex chemistry: most of the grains produced in the Ar/CH4 (95:5) gas mixture ranged from 15 to 385 nm in diameter with an average density of 2.1 grains μm−2, while the grains produced in the Ar/C2H2 (95:5) gas mixture ranged from 40 to 650 nm with a density of 3.5 grains μm−2. Changes in the morphology were also observed, with grains produced from acetylene (C2H2) precursors tending to be more spherical than grains produced from methane (CH4) precursors. This change in morphology could be associated with different stages of growth formation at low temperature from a more "planar" growth at first, followed by coagulation into more spherical particles. This study demonstrates that the COSmIC experimental setup can be used to investigate carbon grain formation from small gas-phase molecular precursors at low temperature (<200 K), i.e., under a temperature regime that is representative of the dust condensation zone and outer region of circumstellar envelopes. [ABSTRACT FROM AUTHOR]

Gas-phase cavity ring-down spectroscopy of jet-cooled benzo[ghi]perylene (C22H12) in the 26 950–28 600-cm-1 spectral range is reported for the first time. This study is part of our extensive laboratory astrophysics program for the study of interstellar polycyclic aromatic hydrocarbons. The observed spectrum shows an intermediate level structure and significant broadening and is associated with the vibronically coupled S1(1A1)←S0(1A1) and S2(1B1)←S0(1A1) electronic transitions. Time-dependent density-functional calculations were performed to calculate the energetics, vibrational frequencies, and normal coordinates of the S1 and S2 states. A simple vibronic model was employed to account for the vibronic interaction between the vibronic levels of the S1 and S2 states. The calculated vibronic spectrum is found to be in good agreement with the experimental spectrum. [ABSTRACT FROM AUTHOR]

As part of our long-term program to test the diffuse interstellar band–polycyclic aromatic hydrocarbon hypothesis, we have investigated the S1←S0 electronic transition of neutral perylene (C20H12) in a combined experimental and theoretical study. Jet-cooled perylene was prepared with a pulsed discharge slit nozzle and detected by cavity ring-down spectroscopy. A number of vibronic features were observed in the 24 000–24 900 cm-1 spectral range. Density functional and ab initio calculations were performed to determine the geometries, harmonic vibrational frequencies, and normal coordinates of both the S0 and S1 electronic states. A rotational temperature of 52±5 K was derived from a rotational contour analysis of the vibronic band associated with the 0-0 transition. A Franck–Condon treatment was carried out to calculate the vibronic spectrum of the S1←S0 transition. A good agreement was found between the calculated and the experimental spectra. A vibrational assignment is proposed and six normal modes are identified. The contribution of neutral compact polycyclic aromatic hydrocarbons to the diffuse interstellar bands is briefly discussed. [ABSTRACT FROM AUTHOR]

The gas-phase electronic absorption spectra of the naphthalene (C[SUB10]H[SUP+,SUB8]) and acenaphthene (C[SUB12]H[SUP+,SUB10])cations have been measured in the visible range in a free jet planar expansion in an attempt to collect data in an astrophysically relevant environment. The direct absorption spectra of two out of four bands measured of the gas-phase cold naphthalene cation along with the gas-phase vibronic absorption spectrum of the cold acenaphthene cation are reported for the first time. Direct absorption spectra of their van der Waals complexes with argon are also reported for the first time. The study has been carried out using the ultrasensitive and versatile technique of cavity ringdown spectroscopy (CRDS) coupled to a pulsed discharge slit nozzle (PDN). The new PDN-CRDS set up is described and its characteristics are evaluated. The direct-absorption spectra of the polycyclic aromatic hydrocarbon (PAH) ions are discussed and compared to the gas-phase and solid-phase data available in the literature. The analysis of the results show that cold, free flying PAH ions are generated in the argon discharge primarily through soft Penning ionization. This enables the intrinsic band profiles to be measured, a key requirement for astrophysical applications. [ABSTRACT FROM AUTHOR]

Here we study the effect of nitrogen insertion on the electronic spectra of polycyclic aromatic hydrocarbon (PAH) molecules measured under laboratory conditions that are relevant for comparison with astronomical data. We examine the case of the substitution of carbon atoms by nitrogen atoms in the benzenoid skeleton of phenanthrene (C14H10), a prototype non-compact PAH. The vibronic transitions of the 2 1 A 1 ( S 1 ) ⟵ X 1 A 1 ( S 0 ) electronic absorption band system of neutral phenanthrene (C14H10) and phenanthridine (C13H9N) molecules seeded in a supersonic free jet expansion of argon gas are measured in the 315-345 nm region using the cavity ring down spectroscopy (CRDS) technique. Additional measurements of the absorption spectra of the phenanthrene, phenanthridine, and 1,10-phenanthroline (C12H8N2) molecules isolated in 10-K solid argon matrices are also presented. The results obtained confirm that laboratory spectra of cold, isolated molecules obtained under astrophysically relevant conditions are required for a direct, unambiguous comparison with astronomical observations as well as for the understanding of the physical evolution of the interstellar medium. [ABSTRACT FROM AUTHOR]

Abstract: To study the correlation between pyrene-like species and the diffuse interstellar bands (DIBs), we have investigated the electronic transitions of 1-pyrenecarboxaldehyde+ and 1-methylpyrene+, which were prepared with a pulsed discharge slit nozzle and detected by cavity ring-down spectroscopy. Several vibronic bands were observed near the λ4428 DIB is detected. Time-dependent density functional theory calculations were performed to aid the assignment of these bands. It is found that none of the observed bands correlate with the λ4428 DIB. The effect of side groups on the vibronic spectrum of pyrene+ is discussed. [Copyright &y& Elsevier]

Multiplex Integrated Cavity Output Spectroscopy (MICOS) is a new cavity-enhanced absorption method that allows the use of broadband dye nanosecond pulsed laser sources and offers a sensitivity equivalent to CRDS. MICOS has been coupled to a pulsed discharge slit nozzle to measure the spectra of the cold naphthalene (C10H8+), acenaphthene (C12H10+) and pyrene (C16H10+) cations in the gas phase. A femtosecond relaxation timescale is measured for the D5←D0 (0–0) transition of C16H10+. Spectra recorded at high plasma energies also show evidence of fragmentation. The CH radical is observed and carbon nanoparticles are generated in the plasma. [Copyright &y& Elsevier]

Reports on the first measurement of a polycyclic aromatic hydrocarbon cation electronic transition in the ultraviolet (UV) spectral region. UV excitation spectrum of the transition of the perylene cation isolated in an argon matrix; Peak of the two-component band.

This paper presents the first results of the solid phase analysis of the Titan tholins generated in the Titan Haze Simulation (THS) experiments. This study complements the gas phase analysis study that was presented in a previous publication introducing the THS capabilities. In the THS experiment, the chemistry is simulated by plasma in the stream of a supersonic jet expansion. With this unique design, the gas is jet-cooled to Titan-like temperature (∼150 K) before inducing the chemistry by plasma, and remains at low temperature in the plasma discharge (∼200 K). Here, we present and discuss the results of scanning electron microscopy and infrared spectroscopy studies of THS solid aerosols produced in the four gas mixtures already studied by mass spectrometry in the gas phase: N 2 CH 4 , N 2 CH 4 C 2 H 2 , N 2 CH 4 C 6 H 6 and N 2 CH 4 C 2 H 2 C 6 H 6 . Differences in the morphology of the grains and aggregates produced in the volume of the gas phase in the plasma cavity, depending on the initial precursors, have been observed by scanning electron microscopy, that appear to be linked to differences in the growth processes and might have an impact on microphysical models. The mid-infrared spectroscopic analysis highlights changes in the nitrogen chemistry, and the abundance of aromatic compounds, depending on the initial gas mixture. A preliminary study of the aging and degradation of the THS samples with time and exposure to air and light has shown the importance, for future studies of laboratory-generated planetary aerosol analogs, of collecting, storing and characterizing samples under controlled environment. A comparison to VIMS data shows that the THS tholins produced in simpler mixtures, i.e., with a higher level of nitrogen incorporation, are more representative of Titan's aerosols. [ABSTRACT FROM AUTHOR]

The aim of the Titan Haze Simulation (THS) experiment is to contribute to a better understanding of aerosol formation in Titan’s atmosphere through the study of the chemical formation pathways that link the simpler gas phase molecules resulting from the first steps of the N 2 –CH 4 chemistry, to the more complex gas phase precursors of aerosols; and more specifically, to investigate the role of polycyclic aromatic hydrocarbons (PAHs) and nitrogenated polycyclic aromatic hydrocarbons (PANHs), among other hydrocarbons, in this process. In the THS experiment developed at the NASA Ames Cosmic simulation facility (COSmIC), Titan’s atmospheric chemistry is simulated by a pulsed plasma jet expansion at temperature conditions (∼150 K) close to those found in Titan’s atmosphere in regions where aerosols are formed. In addition, because of the very short residence time of the gas in the plasma discharge, only the initial steps of the chemistry occur, making the COSmIC/THS a unique tool to study the first and intermediate (when adding heavier precursors to the initial N 2 –CH 4 mixture) steps of Titan’s atmospheric chemistry at low temperature as shown in the study presented here. We further illustrate the potential of COSmIC/THS for the simulation of Titan’s atmospheric chemistry by presenting very promising results from a preliminary comparison of the laboratory data to data from the Cassini Plasma Spectrometer–Ion Beam Spectrometer (CAPS–IBS) instrument. [ABSTRACT FROM AUTHOR]

Abstract: Plasma expansion sources are popular in molecular spectroscopy and in astrochemistry because they generate cold radicals and ions in detectable amounts. The dynamics of a planar flow generated by a pulsed discharge slit nozzle (PDN) have been numerically investigated for a variety of carrier gases seeded with various molecular species. The determination of the bulk flow characteristics is key to a comprehensive modeling of the plasma that is produced in PDN sources. It is found that the flow is established and stabilized within 75 and 25μs when Ar and He are used as carrier gases, respectively. The residence time in the inter-electrode active region is found to be considerably shorter with He than with Ar gas carrier. The detection signal observed upon injection of astrochemical species such as polycylic aromatic hydrocarbons (PAHs) in moderate amounts in the carrier gas exhibits a non linear relation with the initial PAH concentration in the reservoir which is governed by the temperature. The local temperature along the flow axis can be predicted from the initial conditions using the isentropic equation. However, the local pressure and density behavior diverge significantly from an isentropic flow. Finally, implications for the characteristics of the plasma expansion are discussed to help design future laboratory simulations. [Copyright &y& Elsevier]

We present the results of an integrated laboratory and modeling investigation into the impact of stellar X-rays on cosmic dust. Carbonaceous grains were prepared in a cooled (<200 K) supersonic expansion from aromatic molecular precursors, and were later irradiated with 970 eV X-rays. Silicate (enstatite) grains were prepared via laser ablation, thermally annealed, and later irradiated with 500 eV X-rays. Infrared spectra of the 3.4 ÎĽ m band of the carbon sample prepared with benzene revealed 84% ± 5% band area loss for an X-ray dose of 5.2 Ă—1023 eV.cmâˆ'2. Infrared spectra of the 8â€"12 ÎĽ m Siâ€"O band of the silicate sample revealed band area loss up to 63% ± 5% for doses of 2.3 Ă— 1023 eV.cmâˆ'2. A hybrid Monte Carlo particle trajectory approach was used to model the impact of X-rays and ensuing photoelectrons, Auger and collisionally ionized electrons through the bulk. As a result of X-ray ionization and ensuing Coulomb explosions on surface molecules, the calculated mass loss is 60% for the carbonaceous sample and 46% for the silicate sample, within a factor of 2 of the IR band loss, supporting an X-ray induced mass-loss mechanism. We apply the laboratory X-ray destruction rates to estimate the lifetimes of dust grains in protoplanetary disks surrounding 1 M ⊙ and 0.1 M ⊙ G and M stars. In both cases, X-ray destruction timescales are short (a few million years) at the disk surface, but are found to be much longer than typical disk lifetimes (≳10 Myr) over the disk bulk. [ABSTRACT FROM AUTHOR]

Experimental studies are key to investigating the physical and chemical processes that drive cloud and haze formation from gas and solid phase molecular precursors in (exo)planetary environments, and validating the theoretical calculations used in models of (exo)planetary atmospheres. They allow characterizing the physical, optical, and chemical properties of laboratory-generated analogs, hence providing critical input parameters to models for observational data analysis. In this paper, we present examples of (1) experiments performed with different facilities to produce analogs of Titan and exoplanet atmospheric aerosols from gas phase molecular precursors, and (2) the characterization of these analogs to provide information on their composition, morphology, and optical constants to the scientific community. We also introduce the recently launched NASA Center for Optical Constants (NCOC), which will provide this critical data to the scientific community for (exo)planetary-relevant ices and organic refractory materials produced in the laboratory from the irradiation of gas and ice precursors. [ABSTRACT FROM AUTHOR]

Fluorescence spectra of the perylene cation, isolated in an argon matrix and pumped by direct laser excitation via the D[sub 2](²B[sub 3g])←D[sub 0](²A[sub u]) and D[sub 5](²B[sub 3g])←D[sub 0](²A[sub u]) transitions, are presented. Direct excitation into the D[sub 5] or D[sub 2] states is followed by rapid nonradiative relaxation to D[sub 1] that, in turn, relaxes radiatively. Excitation spectroscopy across the D[sub 2](²B[sub 3g])←D[sub 0](²A[sub u]) transition near 730 nm shows that site splitting plays little or no role in determining the spectral substructure in the ion spectra. Tentative assignments for ground state vibrational frequencies are made by a comparison of spectral intervals with calculated normal mode frequencies, with the strongest IR bands leading to the most intense vibronic bands. [ABSTRACT FROM AUTHOR]

The OREOcube (ORganics Exposure inOrbit cube) experiment on theInternational Space Station (ISS) will investigate the effects ofsolar and cosmic radiation on organic thin films supported on inorganicsubstrates. Probing the kinetics of structural changes and photomodulatedorganic–inorganic interactions with real-time in situ UV–visiblespectroscopy, this experiment will investigate the role played bysolid mineral surfaces in the (photo)chemical evolution, transport,and distribution of organics in our solar system and beyond. In preparationfor the OREOcube ISS experiment, we report here laboratory measurementsof the photostability of thin films of the 9,10-anthraquinone derivativeanthrarufin (51 nm thick) layered upon ultrathin films of iron oxidesmagnetite and hematite (4 nm thick), as well as supported directlyon fused silica. During irradiation with UV and visible light simulatingthe photon flux and spectral distribution on the surface of Mars,anthrarufin/iron oxide bilayer thin films were exposed to CO2(800 Pa), the main constituent (and pressure) of the martian atmosphere.The time-dependent photodegradation of anthrarufin thin films revealedthe inhibition of degradation by both types of underlying iron oxidesrelative to anthrarufin on bare fused silica. Interactions betweenthe organic and inorganic thin films, apparent in spectral shiftsof the anthrarufin bands, are consistent with presumed free-electronquenching of semiquinone anion radicals by the iron oxide layers,effectively protecting the organic compound from photodegradation.Combining such in situ real-time kinetic measurements of thin filmsin future space exposure experiments on the ISS with postflight samplereturn and analysis will provide time-course studies complementedby in-depth chemical analysis. This will facilitate the characterizationand modeling of the chemistry of organic species associated with mineralsurfaces in astrobiological contexts. [ABSTRACT FROM AUTHOR]

We have used the Titan Haze Simulation (THS) experimental set-up at NASA Ames' COSmIC facility to produce four laboratory analogs of Titan's aerosols, or tholins. These tholin samples were produced from four gas mixtures of initial compositions N 2 :CH 4 (90:10 and 95:5) and N 2 :CH 4 :C 2 H 2 (89.5:10:0.5 and 94.5:5:0.5) at 150 K, using a plasma discharge in the stream of a jet-cooled gas expansion. Here we present an ex situ X-ray absorption near-edge structure (XANES) spectroscopy analysis of these four tholin samples. The C- and N-XANES spectra show the presence of various functional groups (aromatic carbon, imines, nitriles, etc.) whose abundances are correlated with (i) the relative proportions between N 2 and CH 4 , and (ii) the presence or absence of C 2 H 2 in the initial mixtures. In particular, mixtures containing C 2 H 2 result in the formation of tholins consisting of more aromatic structures and displaying larger relative amounts of imines and nitriles, but lower overall nitrogen content. XANES spectroscopy also allowed for the determination of the elemental C/N ratios for the four tholins, which were all found to be low (< 2.5) and consistent with those measured for tholins produced in other, independent experimental set-ups. The C/N ratios of tholins produced from gas mixtures that contained C 2 H 2 (2.2–2.4) were found to be about twice as large as those of tholins produced from gas mixtures that did not contain C 2 H 2 (0.9–1.3). These new results from the COSmIC/THS experimental set-up demonstrate the impact initial precursors have on the nitrogen chemistry during the formation of tholins, which may help in the interpretation of observations and the development of models of Titan's atmosphere. • Titan aerosol analogs were produced with COSmIC/THS from four gas mixtures. • XANES spectroscopy provided chemical and elemental composition of Titan tholins. • Tholins formed from N 2 :CH 4 and N 2 :CH 4 :C 2 H 2 contain aromatics, imines, and nitriles. • C 2 H 2 resulted in more aromatics, imines, and nitriles, but lower nitrogen content. • Results show effect of initial precursors on nitrogen chemistry in tholin formation. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: The addition of an orthogonal reflectron time-of-flight mass spectrometer (ReTOF-MS) to the NASA Ames cosmic simulation chamber (CSC) experiment is described. The simulation chamber contains the elements that produce the molecular species under astrophysically relevant conditions. A pulsed discharge nozzle (PDN) produces ions, neutrals and radicals in a plasma discharge, which are then expanded and supersonically cooled into the chamber. The coupling of the ReTOF-MS to the CSC provides real-time identification of the species, including cations and neutrals, formed in the plasma, an insight into the chemical pathways of the species reacting in the plasma, and an efficient method for the quick determination of the species present in the plasma, which can then be probed spectroscopically with the cavity ring-down spectrometer (CRDS). The combination of the ReTOF-MS, CRDS and PDN components into a single instrument offers a powerful tool, which can be used to probe a variety of different astrophysical environments such as interstellar clouds and planetary atmospheres. The experimental details and representative mass spectra are presented for plasmas generated in combinations of argon and methane samples. These mass spectra show the unambiguous detection of externally generated ions from the plasma in the simulation chamber. In addition, the various spectra show evidence of fragmentation and bond forming reactivity, illustrating the impact of the composition of the plasma. [Copyright &y& Elsevier]

Abstract: 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 602.45kJm−2 for photons in the range 170–280nm. 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. [Copyright &y& Elsevier]

• The "science-softCon UV/Vis+ photochemistry database" contains EUV-VUV-UV–Vis-NIR spectral data. • The database also contains quantum yields and photolysis related data. • The database provides valuable information for astrophysics, earth and planetary sciences, medical and pharmaceutical sciences. The "science-softCon UV/Vis+ Photochemistry Database" (www.photochemistry.org) is a large and comprehensive collection of EUV-VUV-UV–Vis-NIR spectral data and other photochemical information assembled from published peer-reviewed papers. The database contains photochemical data including absorption, fluorescence, photoelectron, and circular and linear dichroism spectra, as well as quantum yields and photolysis related data that are critically needed in many scientific disciplines. This manuscript gives an outline regarding the structure and content of the "science-softCon UV/Vis+ Photochemistry Database". The accurate and reliable molecular level information provided in this database is fundamental in nature and helps in proceeding further to understand photon, electron and ion induced chemistry of molecules of interest not only in spectroscopy, astrochemistry, astrophysics, Earth and planetary sciences, environmental chemistry, plasma physics, combustion chemistry but also in applied fields such as medical diagnostics, pharmaceutical sciences, biochemistry, agriculture, and catalysis. In order to illustrate this, we illustrate the use of the UV/Vis+ Photochemistry Database in four different fields of scientific endeavor. [ABSTRACT FROM AUTHOR]

The absorption and emission spectra of benzo[g,h,i]perylene, a six ring polycyclic aromatic hydrocarbon molecule (C[sub 22]H[sub 12]), embedded in a rare gas matrix are reported. Time dependent emission shows that this molecule exhibits sharp phosphorescence in the red. Supporting theoretical calculations using the recently developed time-dependent density-functional response theory formalism (TD–DFRT) allow a tentative assignment for the observed transitions. The astrochemical significance of the results is briefly discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]