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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

LOCAL INTERSTELLAR MAGNETIC FIELD DETERMINED FROM THE INTERSTELLAR BOUNDARY EXPLORER RIBBON

The solar wind emanating from the Sun interacts with the local interstellar medium (LISM), forming the heliosphere. Hydrogen energetic neutral atoms (ENAs) produced by the solar-interstellar interaction carry important information about plasma properties from the boundaries of the heliosphere, and are currently being measured by NASA's Interstellar Boundary Explorer (IBEX). IBEX observations show the existence of a “ribbon” of intense ENA emission projecting a circle on the celestial sphere that is centered near the local interstellar magnetic field (ISMF) vector. Here we show that the source of the IBEX ribbon as a function of ENA energy outside the heliosphere, uniquely coupled to the draping of the ISMF around the heliopause, can be used to precisely determine the magnitude (2.93 ± 0.08 μG) and direction (227.°28 ± 0.°69, 34.°62 ± 0.°45 in ecliptic longitude and latitude) of the pristine ISMF far (∼1000 AU) from the Sun. We find that the ISMF vector is offset from the ribbon center by ∼8.°3 toward the direction of motion of the heliosphere through the LISM, and their vectors form a plane that is consistent with the direction of deflected interstellar neutral hydrogen, thought to be controlled by the ISMF. Our results yield draped ISMF properties close to that observed by Voyager 1, the only spacecraft to directly measure the ISMF close to the heliosphere, and give predictions of the pristine ISMF that Voyager 1 has yet to sample.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Determination of interstellar O parameters using the first two years of data from the Interstellar Boundary Explorer

The direct measurements of interstellar matter by the Interstellar Boundary Explorer (IBEX) mission have opened a new and important chapter in our study of the interactions that control the boundaries of our heliosphere. Here we derive for the quantitative information about interstellar O flow parameters from IBEX low-energy neutral atom data for the first time. Specifically, we derive a relatively narrow four-dimensional parameter tube along which interstellar O flow parameters must lie. Along the parameter tube, we find a large uncertainty in interstellar O flow longitude, 76.°0 ± 3.°4 from χ {sup 2} analysis and 76.°5 ± 6.°2 from a maximum likelihood fit, which is statistically consistent with the flow longitude derived for interstellar He, 75.°6 ± 1.°4. The best-fit O and He temperatures are almost identical at a reference flow longitude of 76°, which provides a strong indication that the local interstellar plasma near the Sun is relatively unaffected by turbulent heating. However, key differences include an oxygen parameter tube for the interstellar speed (relation between speed and longitude) that has higher speeds than those in the corresponding parameter tube for He, and an upstream flow latitude for oxygen that is southward of the upstream flow latitude for helium. Both of these differences are likely the result of enhanced filtration of interstellar oxygen due to its charge-exchange ionization rate, which is higher than that for helium. Furthermore, we derive an interstellar O density near the termination shock of 5.8{sub −0.8}{sup +0.9}×10{sup −5} cm{sup −3} that, within uncertainties, is consistent with previous estimates. Thus, we use IBEX data to probe the interstellar properties of oxygen.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Charting the interstellar magnetic field causing the interstellar boundary explorer (IBEX) ribbon of energetic neutral atoms

The interstellar magnetic field (ISMF) near the heliosphere is a fundamental component of the solar galactic environment that can only be studied using polarized starlight. The results of an ongoing survey of the linear polarizations of local stars are analyzed with the goal of linking the ISMF that shapes the heliosphere to the nearby field in interstellar space. We present new results on the direction of the magnetic field within 40 pc obtained from analyzing polarization data using a merit function that determines the field direction that provides the best fit to the polarization data. Multiple magnetic components are identified, including a dominant interstellar field, B{sub POL}, that is aligned with the direction ℓ, b = 36.°2, 49.°0 (±16.°0). Stars tracing B{sub POL} have the same mean distance as stars that do not trace B{sub POL}, but show weaker average polarizations consistent with a smaller column density of polarizing material. B{sub POL} is aligned with the ISMF traced by the IBEX Ribbon to within 7.6{sub −7.6}{sup +14.9} degrees. The variations in the polarization position angle directions derived from the data that best match B{sub POL} indicate a low level of magnetic turbulence, ∼9° ± 1°. The direction of B{sub POL} is obtained after excluding polarization data tracing a separate magnetic structure that appears to be associated with interstellar dust deflected around the heliosphere. The velocities of local interstellar clouds relative to the Local Standard of Rest (LSR) increase with the angles between the LSR velocities and B{sub POL}, indicating that the kinematics of local interstellar material is ordered by the ISMF. The Loop I superbubble that extends close to the Sun contains dust that reddens starlight and whose distance is determined by the color excess E(B − V) of starlight. Polarizations caused by grains aligned with respect to B{sub POL} are consistent with the location of the Sun in the rim of the Loop I superbubble. An angle of 76.8{sub −27.6}{sup +23.5} between B{sub POL} and the bulk LSR velocity the local interstellar material indicates a geometry that is consistent with an expanding superbubble. The efficiency of grain alignment in the local interstellar medium has been assessed using stars where both polarization data and hydrogen column density data are available. Nearby stars appear to have larger polarizations than expected based on reddened sightlines, which is consistent with previous results, but uncertainties are large. Optical polarization and color excess E(B − V) data indicate the presence of nearby interstellar dust in the BICEP2 field. Color excess E(B − V) indicates an optical extinction of A{sub V} > 0.6 in the BICEP2 field, while the polarization data indicate that A{sub V} > 0.09 mag. The IBEX Ribbon ISMF extends to the boundaries of the BICEP2 region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope Data

Most of the celestial γ rays detected by the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope originate from the interstellar medium when energetic cosmic rays interact with interstellar nucleons and photons. Conventional point and extended source studies rely on the modeling of this diffuse emission for accurate characterization. We describe here the development of the Galactic Interstellar Emission Model (GIEM) that is the standard adopted by the LAT Collaboration and is publicly available. The model is based on a linear combination of maps for interstellar gas column density in Galactocentric annuli and for the inverse Compton emission produced in the Galaxy. We also include in the GIEM large-scale structures like Loop I and the Fermi bubbles. The measured gas emissivity spectra con rm that the cosmic-ray proton density decreases with Galactocentric distance beyond 5 kpc from the Galactic Center. The measurements also suggest a softening of the proton spectrum with Galactocentric distance. We observe that the Fermi bubbles have boundaries with a shape similar to a catenary at latitudes below 20° and we observe an enhanced emission toward their base extending in the North and South Galactic direction and located within ~4° of the Galactic Center.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

GAS PHASE SYNTHESIS OF (ISO)QUINOLINE AND ITS ROLE IN THE FORMATION OF NUCLEOBASES IN THE INTERSTELLAR MEDIUM

Nitrogen-substituted polycyclic aromatic hydrocarbons (NPAHs) have been proposed to play a key role in the astrochemical evolution of the interstellar medium, yet the formation mechanisms of even their simplest prototypes—quinoline and isoquinoline—remain elusive. Here, we reveal a novel concept that under high temperature conditions representing circumstellar envelopes of carbon stars, (iso)quinoline can be synthesized via the reaction of pyridyl radicals with two acetylene molecules. The facile gas phase formation of (iso)quinoline in circumstellar envelopes defines a hitherto elusive reaction class synthesizing aromatic structures with embedded nitrogen atoms that are essential building blocks in contemporary biological-structural motifs. Once ejected from circumstellar shells and incorporated into icy interstellar grains in cold molecular clouds, these NPAHs can be functionalized by photo processing forming nucleobase-type structures as sampled in the Murchison meteorite.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

SIMULATIONS OF A DYNAMIC SOLAR CYCLE AND ITS EFFECTS ON THE INTERSTELLAR BOUNDARY EXPLORER RIBBON AND GLOBALLY DISTRIBUTED ENERGETIC NEUTRAL ATOM FLUX

Since 2009, observations by the Interstellar Boundary Explorer (IBEX) have vastly improved our understanding of the interaction between the solar wind (SW) and local interstellar medium through direct measurements of energetic neutral atoms (ENAs), which inform us about the heliospheric conditions that produced them. An enhanced feature of flux in the sky, the so-called IBEX ribbon, was not predicted by any global models before the first IBEX observations. A dominating theory of the origin of the ribbon, although still under debate, is a secondary charge-exchange process involving secondary ENAs originating from outside the heliopause. According to this mechanism, the evolution of the solar cycle should be visible in the ribbon flux. Therefore, in this paper we simulate a fully time-dependent ribbon flux, as well as globally distributed flux from the inner heliosheath (IHS), using time-dependent SW parameters from Sokół et al. as boundary conditions for our time-dependent heliosphere simulation. After post-processing the results to compute H ENA fluxes, our results show that the secondary ENA ribbon indeed should be time dependent, evolving with a period of approximately 11 yr, with differences depending on the energy and direction. Our results for the IHS flux show little periodic change with the 11 yr solar cycle, but rather with short-term fluctuations in the background plasma. While the secondary ENA mechanism appears to emulate several key characteristics of the observed IBEX ribbon, it appears that our simulation does not yet include all of the relevant physics that produces the observed ribbon.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE C({sup 3}P) + NH{sub 3} REACTION IN INTERSTELLAR CHEMISTRY. I. INVESTIGATION OF THE PRODUCT FORMATION CHANNELS

The product formation channels of ground state carbon atoms, C({sup 3}P), reacting with ammonia, NH{sub 3}, have been investigated using two complementary experiments and electronic structure calculations. Reaction products are detected in a gas flow tube experiment (330 K, 4 Torr) using tunable vacuum-ultraviolet (VUV) photoionization coupled with time of flight mass spectrometry. Temporal profiles of the species formed and photoionization spectra are used to identify primary products of the C + NH{sub 3} reaction. In addition, H-atom formation is monitored by VUV laser induced fluorescence (LIF) from room temperature to 50 K in a supersonic gas flow generated by the Laval nozzle technique. Electronic structure calculations are performed to derive intermediates, transition states, and complexes formed along the reaction coordinate. The combination of photoionization and LIF experiments supported by theoretical calculations indicate that in the temperature and pressure range investigated, the H + H{sub 2}CN production channel represents 100% of the product yield for this reaction. Kinetics measurements of the title reaction down to 50 K and the effect of the new rate constants on interstellar nitrogen hydride abundances using a model of dense interstellar clouds are reported in Paper II.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Dust-polarization Maps and Interstellar Turbulence

Perhaps the most intriguing result of Planck’s dust-polarization measurements is the observation that the power in the E-mode polarization is twice that in the B mode, as opposed to pre-Planck expectations of roughly equal dust powers in the E and B modes. Here we show how the E- and B-mode powers depend on the detailed properties of the fluctuations in the magnetized interstellar medium (ISM). These fluctuations can be decomposed into slow, fast, and Alfvén magnetohydrodynamic (MHD) waves, which comprise a complete basis that can be used to describe linear fluctuations of a magnetized fluid. They can alternatively be decomposed in terms of one longitudinal and two transverse components of a fluid-displacement field. The intensity (T) and E- and B-mode amplitudes induced by each of the three types of waves, in both decompositions, are then calculated. To illustrate how these tools can be applied, we consider a toy model of the ISM in which dust traces a single component of plasma, and obtain the EE/BB ratio and TE correlation for several ansatzes for the power in slow/fast/Alfvén waves and in longitudinal/transverse waves. Although our model may be too simplistic to properly describe the nonlinear structure of interstellar magnetic fields, we find that the observed EE/BB ratio (and its scale invariance) and positive TE correlation—as well as the observed power-law index for the angular spectrum of these fluctuations—are not easily accommodated in terms of simple MHD turbulence prescriptions for the expected powers in slow, fast, and Alfvén waves. We speculate that the ∼0.1–30 pc length scales probed by these dust-polarization measurements are not described by MHD turbulence, but rather probe the large-scale physics that drives ISM turbulence. We find that a slightly anisotropic spectrum of random fluid displacements produces EE/BB≃2 and a positive TE cross-correlation. Furthermore, we find that large EE/BB and positive TE are due primarily to longitudinal, rather than transverse, modes in the random-displacement field, providing, perhaps, some clue to the mechanism that stirs the ISM. Future investigations involving the spatial dependence of the EE/BB ratio, TE correlation, and local departures from statistical isotropy in dust-polarization maps, as well as further tests of some of the assumptions in this analysis, are outlined. This work may also aid in the improvement of foreground-separation techniques for studies of cosmic microwave background polarization.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

STRUCTURE OF THE INTERSTELLAR BOUNDARY EXPLORER RIBBON FROM SECONDARY CHARGE-EXCHANGE AT THE SOLAR–INTERSTELLAR INTERFACE

In 2009, the Interstellar Boundary Explorer discovered a bright “ribbon” of energetic neutral atom (ENA) flux in the energy range ≤0.4–6 keV, encircling a large portion of the sky. This observation was not previously predicted by any models or theories, and since its discovery, it has been the subject of numerous studies of its origin and properties. One of the most studied mechanisms for its creation is the “secondary ENA” process. Here, solar wind ions, neutralized by charge-exchange with interstellar atoms, propagate outside the heliopause; experience two charge-exchange events in the dense outer heliosheath; and then propagate back inside the heliosphere, preferentially in the direction perpendicular to the local interstellar magnetic field. This process has been extensively analyzed using state-of-the-art modeling and simulation techniques, but it has been difficult to visualize. In this Letter, we show the three-dimensional structure of the source of the ribbon, providing a physical picture of the spatial and energy scales over which the secondary ENA process occurs. These results help us understand how the ribbon is generated and further supports a secondary ENA process as the leading ribbon source mechanism.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Diffuse interstellar bands versus known atomic and molecular species in the interstellar medium of M82 toward SN 2014J

We discuss the absorption due to various constituents of the interstellar medium (ISM) of M82 seen in moderately high-resolution, high signal-to-noise ratio optical spectra of SN 2014J. Complex absorption from M82 is seen, at velocities 45 ≲ v {sub LSR} ≲ 260 km s{sup –1}, for Na I, K I, Ca I, Ca II, CH, CH{sup +}, and CN; many of the diffuse interstellar bands (DIBs) are also detected. Comparisons of the column densities of the atomic and molecular species and the equivalent widths of the DIBs reveal both similarities and differences in relative abundances, compared to trends seen in the ISM of our Galaxy and the Magellanic Clouds. Of the 10 relatively strong DIBs considered here, 6 (including λ5780.5) have strengths within ±20% of the mean values seen in the local Galactic ISM, for comparable N(K I); 2 are weaker by 20%-45% and 2 (including λ5797.1) are stronger by 25%-40%. Weaker than 'expected' DIBs (relative to N(K I), N(Na I), and E(B – V)) in some Galactic sight lines and toward several other extragalactic supernovae appear to be associated with strong CN absorption and/or significant molecular fractions. While the N(CH)/N(K I) and N(CN)/N(CH) ratios seen toward SN 2014J are similar to those found in the local Galactic ISM, the combination of high N(CH{sup +})/N(CH) and high W(5797.1)/W(5780.5) ratios has not been seen elsewhere. The centroids of many of the M82 DIBs are shifted relative to the envelope of the K I profile—likely due to component-to-component variations in W(DIB)/N(K I) that may reflect the molecular content of the individual components. We compare estimates for the host galaxy reddening E(B – V) and visual extinction A {sub V} derived from the various interstellar species with the values estimated from optical and near-IR photometry of SN 2014J.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

MAPPING THE INTERSTELLAR MEDIUM WITH NEAR-INFRARED DIFFUSE INTERSTELLAR BANDS

We map the distribution and properties of the Milky Way's interstellar medium as traced by diffuse interstellar bands (DIBs) detected in near-infrared stellar spectra from the SDSS-III/APOGEE survey. Focusing exclusively on the strongest DIB in the H band, at λ ∼ 1.527 μm, we present a projected map of the DIB absorption field in the Galactic plane, using a set of about 60,000 sightlines that reach up to 15 kpc from the Sun and probe up to 30 mag of visual extinction. The strength of this DIB is linearly correlated with dust reddening over three orders of magnitude in both DIB equivalent width (W {sub DIB}) and extinction, with a power law index of 1.01 ± 0.01, a mean relationship of W {sub DIB}/A{sub V} = 0.1 Å mag{sup –1} and a dispersion of ∼0.05 Å mag{sup –1} at extinctions characteristic of the Galactic midplane. These properties establish this DIB as a powerful, independent probe of dust extinction over a wide range of A{sub V} values. The subset of about 14,000 robustly detected DIB features have a W {sub DIB} distribution that follows an exponential trend. We empirically determine the intrinsic rest wavelength of this transition to be λ{sub 0} = 15 272.42 Å and use it to calculate absolute radial velocities of the carrier, which display the kinematical signature of the rotating Galactic disk. We probe the DIB carrier distribution in three dimensions and show that it can be characterized by an exponential disk model with a scale height of about 100 pc and a scale length of about 5 kpc. Finally, we show that the DIB distribution also traces large-scale Galactic structures, including the Galactic long bar and the warp of the outer disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

A SURVEY OF MAGNETIC WAVES EXCITED BY NEWBORN INTERSTELLAR He{sup +} OBSERVED BY THE ACE SPACECRAFT AT 1 au

We report observations of low-frequency waves at 1 au by the magnetic field instrument on the Advanced Composition Explorer ( ACE /MAG) and show evidence that they arise due to newborn interstellar pickup He{sup +}. Twenty-five events are studied. They possess the generally predicted attributes: spacecraft-frame frequencies slightly greater than the He{sup +} cyclotron frequency, left-hand polarization in the spacecraft frame, and transverse fluctuations with minimum variance directions that are quasi-parallel to the mean magnetic field. Their occurrence spans the first 18 years of ACE operations, with no more than 3 such observations in any given year. Thus, the events are relatively rare. As with past observations by the Ulysses and Voyager spacecraft, we argue that the waves are seen only when the background turbulence is sufficiently weak as to allow for the slow accumulation of wave energy over many hours.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Quantifying the interstellar medium and cosmic rays in the MBM 53, 54, and 55 molecular clouds and the pegasus loop using Fermi-LAT gamma-ray observations

A study of the interstellar medium (ISM) and cosmic rays (CRs) using Fermi Large Area Telescope (LAT) data, in a region encompassing the nearby molecular clouds MBM 53, 54, and 55 and a far-infrared loop-like structure in Pegasus, is reported. By comparing the Planck dust thermal emission model with Fermi-LAT γ-ray data, it was found that neither the dust radiance (R) nor the dust opacity at 353 GHz (τ {sub 353}) was proportional to the total gas column density N(H{sub tot}) primarily because N(H{sub tot})/R and N(H{sub tot})/τ {sub 353} depend on the dust temperature (T {sub d}). The N(H{sub tot}) distribution was evaluated using γ-ray data by assuming the regions of high T {sub d} to be dominated by optically thin atomic hydrogen (H I) and by employing an empirical linear relation of N(H{sub tot})/R to T {sub d}. It was determined that the mass of the gas not traced by the 21 cm or 2.6 mm surveys is ∼25% of the mass of H I in the optically thin case and is larger than the mass of the molecular gas traced by carbon monoxide by a factor of up to 5. The measured γ-ray emissivity spectrum is consistent with a model based on CR spectra measured at the Earth and a nuclear enhancement factor of ≤1.5. It is, however, lower than local H I emissivities reported by previous Fermi-LAT studies employing different analysis methods and assumptions on ISM properties by 15%–20% in energies below a few GeV, even if we take account of the statistical and systematic uncertainties. The origin of the discrepancy is also discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Latitudinal and energy dependence of energetic neutral atom spectral indices measured by the Interstellar Boundary Explorer

We investigate the latitudinal and energy dependence of the globally distributed 0.5–6 keV energetic neutral atom (ENA) spectra measured by the Interstellar Boundary Explorer (IBEX) during the first 3 yrs of the mission. Our results are: (1) the ENA spectral indices at the two lowest energies (0.89 and 1.47 keV) exhibit no clear trend with ecliptic latitude θ, while those at ∼2.29 and ∼3.41 keV exhibit a clear latitudinal pattern; flatter spectra occur above 60° latitude and steeper spectra occur ±30° of the equator. (2) The latitudinal dependence of the spectral indices at different energies can be represented by the cosine function γ=a{sub 0}+a{sub 1}cos(a{sub 2}θ) with unique offsets, amplitudes, and phase angles; the higher energy ENA indices transition to successively larger amplitudes within ±45° of the equator. Our results confirm the previously reported latitudinal organization of the ENA spectra and their remarkable similarity to that of the solar wind (SW) speed observed by Ulysses in the inner heliosphere. While earlier studies showed that the ∼0.5–6 keV globally distributed ENA spectral indices could be represented as single power laws over much of the sky, our new results indicate that this is an over-simplification because the spectral indices have an energy and latitude dependence. This dependence is an important factor that must be taken into consideration by models and simulations that seek to map the IBEX ENA observations back to the latitudinal profile of the SW speed structure observed in the inner heliosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE C({sup 3}P) + NH{sub 3} REACTION IN INTERSTELLAR CHEMISTRY. II. LOW TEMPERATURE RATE CONSTANTS AND MODELING OF NH, NH{sub 2}, AND NH{sub 3} ABUNDANCES IN DENSE INTERSTELLAR CLOUDS

A continuous supersonic flow reactor has been used to measure rate constants for the C({sup 3}P) + NH{sub 3} reaction over the temperature range 50–296 K. C({sup 3}P) atoms were created by the pulsed laser photolysis of CBr{sub 4}. The kinetics of the title reaction were followed directly by vacuum ultra-violet laser induced fluorescence of C({sup 3}P) loss and through H({sup 2}S) formation. The experiments show unambiguously that the reaction is rapid at 296 K, becoming faster at lower temperatures, reaching a value of (1.8 ± 0.2) × 10{sup −10} cm{sup 3} molecule{sup −1} s{sup −1} at 50 K. As this reaction is not currently included in astrochemical networks, its influence on interstellar nitrogen hydride abundances is tested through a dense cloud model including gas–grain interactions. In particular, the effect of the ortho-to-para ratio of H{sub 2}, which plays a crucial role in interstellar NH{sub 3} synthesis, is examined.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

On the formation of nitrogen-substituted polycyclic aromatic hydrocarbons (NPAHs) in circumstellar and interstellar environments

The chemical evolution of extraterrestrial environments leads to the formation of polycyclic aromatic hydrocarbons (PAHs) via gas phase radical mediated aromatization reactions. Here, we review that these de facto barrierless reactions are capable of forming prebiotic molecules such as nitrogen substituted PAHs (NPAHs), which represent the missing link between nitrogen bearing acyclic molecules and prebiotic nucleobases along with vitamins found in meteorites. Crucial routes leading to the incorporation of nitrogen atoms into the aromatic ring have been exposed. Pyridine can be formed from the reaction of abundant vinyl cyanide and its radical or via cyano radicals reacting with 1,3-butadiene. The NPAHs 1,4-dihydro(iso)quinoline and (iso)quinoline can be synthesized through reaction of pyridyl radicals with 1,3-butadiene or sequentially with two acetylene molecules, respectively. The inclusion of nitrogen into an aromatic system and their growth can fill the mechanistic gaps missing leading from acyclic nitrogen-bearing molecules via pyridine to NPAH-type molecules in the interstellar medium.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗