scholarly journals On carbon nanotubes in the interstellar medium

2020 ◽  
Vol 493 (2) ◽  
pp. 3054-3059
Author(s):  
Qi Li ◽  
Aigen Li ◽  
B W Jiang ◽  
Tao Chen
Keyword(s):  
Carbon Nanotubes ◽  
Interstellar Medium ◽  
Interstellar Extinction ◽  
Extinction Curve ◽  
Interstellar Space ◽  
Absorption Bands ◽  
Carbon Allotrope ◽  
Wide Range ◽  
Polycyclic Aromatic ◽  
The Universe

ABSTRACT Since their discovery in 1991, carbon nanotubes (CNTs) – a novel one-dimensional carbon allotrope – have attracted considerable interest worldwide because of their potential technological applications such as electric and optical devices. In the astrophysical context, CNTs may be present in the interstellar space since many of the other allotropes of carbon (e.g. amorphous carbon, fullerenes, nanodiamonds, graphite, polycyclic aromatic hydrocarbons, and possibly graphene as well) are known to be widespread in the Universe, as revealed by pre-solar grains in carbonaceous primitive meteorites and/or by their fingerprint spectral features in astronomical spectra. In addition, there are also experimental and theoretical pathways to the formation of CNTs in the interstellar medium (ISM). In this work, we examine their possible presence in the ISM by comparing the observed interstellar extinction curve with the ultraviolet/optical absorption spectra experimentally obtained for single-walled CNTs of a wide range of diameters and chiralities. Based on the absence in the interstellar extinction curve of the ${\sim}$4.5 and 5.25 ${\rm eV} \ \pi$-plasmon absorption bands that are pronounced in the experimental spectra of CNTs, we place an upper limit of ${\sim}10\, {\rm ppm}$ of C/H (i.e. ${\sim}$4 per cent of the total interstellar C) on the interstellar CNT abundance.

scholarly journals Grains in Diffuse Clouds: Carbon-Coated Silicate Cores

1989 ◽  
Vol 135 ◽  
pp. 367-373
Author(s):  
David A. Williams
Keyword(s):  
Interstellar Medium ◽  
Amorphous Carbon ◽  
Laboratory Data ◽  
Interstellar Extinction ◽  
Extinction Curve ◽  
Total Carbon ◽  
Small Radius ◽  
Carbon Coatings ◽  
Wide Range ◽  
Diffuse Clouds

A new model of interstellar grains is proposed in which grains in diffuse clouds consist of small (radius ≲ 10nm) and large asymmetric (0.05μm – 0.25μm) silicate cores thinly coated with mantles of amorphous carbon (thickness ≲ 5nm). This model can account successfully for many of the observed properties of interstellar dust and gives a simple interpretation of the interstellar extinction curve. The extinction bump at 220nm is attributed to absorption by finely divided silicates, as indicated by laboratory data. The large silicates provide a “grey” background extinction through the visual and UV, but the bulk of the extinction in this region is attributed, on the basis of laboratory data, to the amorphous carbon coatings. The average interstellar carbon depletion required in this model is about 50%.Wide variations in the observed interstellar extinction along different lines of sight are well known. These variations have a natural explanation in this model in terms of two parameters: the thickness of the carbon coatings, and the proportion of graphitic to diamond-like structure within the amorphous carbon. The underlying silicate cores are generally unchanged in these variations. The average interstellar extinction curve requires roughly equal proportions of graphitic and diamond-like forms of amorphous carbon. A higher graphitic fraction produces more visual extinction and a higher diamond-like fraction produces more far UV extinction. Varying both the proportions, and the total carbon content encompasses a wide range of extinction curve shapes.Amorphous carbon deposited at low temperature is generally diamond-like. Temperature excursions in the material reduce the hydrogen content and enhance the graphitic nature of the material. In the interstellar medium, this process has a time scale ≳ 106 yr. Carbon coatings are therefore expected to be deposited in the interstellar medium in diamond-like form and to be slowly converted to graphitelike. The growth of carbon mantles will be reversed by intermittent shocks Thus, interstellar space should contain grains with a range of thicknesses of carbon coatings, and compositions between graphitic and diamond-like.The chemical and physical properties of amorphous carbon have been the subject of intensive laboratory study. These properties enable an understanding of a variety of observations of dust (especially in the IR) and lead to a number of predictions which are described in this paper.

scholarly journals Probing the missing link between the diffuse interstellar bands and the total-to-selective extinction ratio $R_V\,\!-\!$ I. Extinction versus reddening

2019 ◽  
Vol 489 (1) ◽  
pp. 708-713 ◽  
Author(s):  
Kaijun Li ◽  
Aigen Li ◽  
F Y Xiang
Keyword(s):  
Extinction Ratio ◽  
Interstellar Extinction ◽  
Extinction Curve ◽  
Interstellar Clouds ◽  
Diffuse Interstellar Bands ◽  
Hydrogen Column Density ◽  
Wide Range ◽  
Chemical Conditions ◽  
Physical And Chemical ◽  
Selective Extinction

ABSTRACT The carriers of the still (mostly) unidentified diffuse interstellar bands (DIBs) have been a long-standing mystery ever since their first discovery exactly 100 yr ago. In recent years, the ubiquitous detection of a large number of DIBs in a wide range of Galactic and extragalactic environments has led to renewed interest in connecting the occurrence and properties of DIBs to the physical and chemical conditions of the interstellar clouds, with particular attention paid to whether the DIB strength is related to the shape of the interstellar extinction curve. To shed light on the nature and origin of the DIB carriers, we investigate the relation between the DIB strength and RV, the total-to-selective extinction ratio, which characterizes how the extinction varies with wavelength (i.e. the shape of the extinction curve). We find that the DIB strength and RV are not related if we represent the strength of a DIB by its reddening-normalized equivalent width (EW), in contrast to the earlier finding of an anticorrelation in which the DIB strength is measured by the extinction-normalized EW. This raises a fundamental question about the appropriate normalization for the DIB EW. We argue that the hydrogen column density is a more appropriate normalization than extinction and reddening.

scholarly journals Detection of the aromatic molecule benzonitrile (c-C6H5CN) in the interstellar medium

Science ◽  
2018 ◽  
Vol 359 (6372) ◽  
pp. 202-205 ◽  
Author(s):  
Brett A. McGuire ◽  
Andrew M. Burkhardt ◽  
Sergei Kalenskii ◽  
Christopher N. Shingledecker ◽  
Anthony J. Remijan ◽  
...  
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Polycyclic Aromatic Hydrocarbon ◽  
Interstellar Medium ◽  
Aromatic Hydrocarbon ◽  
Aromatic Hydrocarbons ◽  
Nitrogen Heterocycles ◽  
Aromatic Molecules ◽  
Polycyclic Aromatic ◽  
Hydrocarbon Formation ◽  
The Universe

Polycyclic aromatic hydrocarbons and polycyclic aromatic nitrogen heterocycles are thought to be widespread throughout the universe, because these classes of molecules are probably responsible for the unidentified infrared bands, a set of emission features seen in numerous Galactic and extragalactic sources. Despite their expected ubiquity, astronomical identification of specific aromatic molecules has proven elusive. We present the discovery of benzonitrile (c-C6H5CN), one of the simplest nitrogen-bearing aromatic molecules, in the interstellar medium. We observed hyperfine-resolved transitions of benzonitrile in emission from the molecular cloud TMC-1. Simple aromatic molecules such as benzonitrile may be precursors for polycyclic aromatic hydrocarbon formation, providing a chemical link to the carriers of the unidentified infrared bands.

scholarly journals Search of amino group in the Universe: 2-aminopyridine

2015 ◽  
pp. 81-86
Author(s):  
M.K. Sharma ◽  
M. Sharma ◽  
A.K. Sharma ◽  
S. Chandra
Keyword(s):  
Amino Acid ◽  
Interstellar Medium ◽  
Galactic Center ◽  
Close Association ◽  
Spectroscopic Studies ◽  
Interstellar Space ◽  
Amino Group ◽  
The Earth ◽  
The Universe ◽  
Amino Acid Glycine

In search for life in the Universe, scientists are interested in identification of molecules having amino (-NH2) group in the interstellar space. The aminoacetonitrile (NH2CH2CN), which is precursor of the simplest amino acid glycine (NH2CH2COOH), is identified near the galactic center. The 2-Aminopyridine (H2NC5H4N) is of interest for scientists as it has a close association with life on the earth. Based on spectroscopic studies, we have calculated intensities of 2-Aminopyridine lines due to transitions between the rotational levels up to 47 cm?1 and have found a number of lines which may help in its identification in the interstellar medium. Frequencies of some of these transitions are found close to those detected in the envelope of IRC +10216 that are not assigned to any of the known species.

scholarly journals On buckyonions as a carrier of the 2175 Å interstellar extinction feature

2008 ◽  
Vol 4 (S251) ◽  
pp. 71-72 ◽  
Author(s):  
Juhua Chen ◽  
Moping Li ◽  
Aigen Li ◽  
Yongjiu Wang
Keyword(s):  
Interstellar Medium ◽  
Amorphous Carbon ◽  
Electronic Transition ◽  
Interstellar Extinction ◽  
Extinction Curve ◽  
Close Similarity ◽  
Upper Limit ◽  
Dust Component ◽  
Feature Based ◽  
Extinction Feature

AbstractIn recent years buckyonions have been suggested as a carrier of the 2175 Å interstellar extinction feature, based on the close similarity between the electronic transition spectra of buckyonions and the 2175 Å interstellar extinction feature. We examine this hypothesis by calculating the interstellar extinction with buckyonions as a dust component. It is found that dust models containing buckyonions (in addition to amorphous silicates, PAHs, graphite or amorphous carbon) can closely reproduce the observed interstellar extinction curve. However, a more severe challenge to the buckyonion hypothesis is provided by the non-detection of the ~7–8 μm C–H stretching bands expected from buckyonions in the diffuse interstellar medium. This will allow us to place an upper limit on the abundance of buckyonions.

scholarly journals Extinction curves for graphite-silicate grain mixtures

1970 ◽  
Vol 36 ◽  
pp. 42-49
Author(s):  
N.C. Wickramasinghe
Keyword(s):  
Interstellar Medium ◽  
Wavelength Range ◽  
Mass Density ◽  
Interstellar Extinction ◽  
Extinction Curve ◽  
Carbon Stars ◽  
Graphite Particles ◽  
Order Of Magnitude ◽  
Entire Wavelength Range ◽  
Comparable Mass

Mixtures of graphite particles ejected from carbon stars and silicates from oxygen-rich giants are capable of producing excellent fits to the observed interstellar extinction curve. The fits extend over the entire wavelength range of the observations, and include a hump at ~ 2200 Å in the ultraviolet due to the graphite components of the mixtures. The agreement with the observed extinction curve remains good if the small silicate particles acquire mantles of either ice or solid H2. If no mantles are present around the silicate grains comparable mass densities of graphite and silicates are indicated; if mantles of either ice or solid H2 are present the mass density of silicates may be an order of magnitude below that of graphite in the interstellar medium.

scholarly journals Theoretical Investigation of PAHs: Implications to Diffuse Interstellar Bands

2013 ◽  
Vol 9 (S297) ◽  
pp. 349-352 ◽  
Author(s):  
A. Pathak ◽  
M. Buragohain ◽  
M. Hammonds ◽  
P. J. Sarre
Keyword(s):  
Density Functional ◽  
Visible Region ◽  
Interstellar Extinction ◽  
Interstellar Space ◽  
Strongly Correlated ◽  
Molecular Systems ◽  
Large Molecules ◽  
Tddft Calculations ◽  
Diffuse Interstellar Bands ◽  
Polycyclic Aromatic

AbstractAbout a thousand optical absorption features on the interstellar extinction curve popularly known as the Diffuse Interstellar Bands (DIBs) have been observed. The numbers are increasing every year, thanks to the improvement in telescope and spectroscopic technology. Ultra-high resolution spectroscopic observations and emission features corresponding to some of the DIBs suggest that, some if not all, of these features are due to large molecules. The strength of DIBs depend on the amount of reddening which is directly proportional to the amount of material present between the background star and the observer. Since, the strengths of the DIBs are not strongly correlated with each other, there must be several carriers. Time Dependent Density Functional Theory (TDDFT) calculations are useful in narrowing down molecular systems that may be further investigated in the laboratory.The observations of the unidentified infrared (UIR) bands point towards the widespread presence of Polycyclic Aromatic Hydrocarbon (PAH) molecules. Though, not a single PAH has been discovered in interstellar space, these are the largest molecules suspected to be present. PAHs are stable towards energetic environment prevailing under interstellar conditions rendering these molecules to be good candidates as DIB carriers. We report TDDFT calculations to predict electronic transitions of neutral, protonated-deuteronated and PAHs with five member rings with various sites of protonation and deuteronation. Compared to their neutral forms, these charged isoelectronic forms of PAHs are predicted to have active transitions in the visible region, which means they are suitable candidates as carriers for some of the DIBs and laboratory studies are warranted for these systems.

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