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The RNA world hypothesis suggests that early cellular ancestors relied solely on RNA molecules for both genetic information storage and cellular functions. RNA, composed of four nucleosides—adenosine, guanosine, cytidine, and uridine—forms the basis of this theory. These nucleosides consist of purine nucleobases, adenine and guanine, and pyrimidine nucleobases, cytosine and uracil, bonded to ribose sugar. Notably, carbonaceous chondrite meteorites have revealed the presence of these bases and sugar, hinting at the potential existence of nucleosides in space. This study aims to present the infrared spectra of four RNA nucleosides commonly found in terrestrial biochemistry, facilitating their detection in space, especially in astrobiological and astrochemical contexts. Laboratory measurements involved obtaining mid- and far-IR spectra at three temperatures (−180 °C, room temperature, and +180 °C), followed by calculating molar extinction coefficients (ε) and integrated molar absorptivities (ψ) for corresponding bands. These spectral data, along with ε and ψ values, serve to provide quantitative insights into the presence and relative abundance of nucleosides in space and aid in their detection. [ABSTRACT FROM AUTHOR]

We have used spectra of the Spitzer Space Telescope to conduct a search for the aromatic amino acid tryptophan in the interstellar gas of the young star cluster IC 348. For all the strongest mid-infrared (mid-IR) laboratory bands of tryptophan, we have found counterpart emission lines in the observed spectrum which are consistent in wavelength and strength with the laboratory measurements. Assuming that the detected emission lines are due to tryptophan and using the measured fluxes, we estimate a tryptophan column density in the line of sight of the core of IC 348 in the range 109–1011 cm−2. The observed emission lines are also found in the combined spectrum of >30 interstellar locations obtained in diverse unrelated star-forming regions observed by Spitzer. This could be an indication that the molecule causing the emission is widespread in interstellar space. Future high spectral resolution mid-IR searches for proteinogenic amino acids in protostars, protoplanetary discs, and in the interstellar medium will be key to study an exogenous origin of meteoritic amino acids and to understand how the pre-biotic conditions for life were set in the early Earth. [ABSTRACT FROM AUTHOR]

The nucleobases, namely the purines adenine and guanine and the pyrimidines cytosine, thymine, and uracil, are the key monomers of the information polymers DNA and RNA. All the nucleobases were recently detected in the analysis of certain meteorites known as carbonaceous chondrites. The concentration of the nucleobases found in meteorites is smaller than the concentration of amino acids. However, the nucleobases were successfully synthesized abiotically by ultraviolet irradiation of interstellar ice analogues at 10 K. Consequently, it is possible that the purines and pyrimidines may be present in the interstellar medium or in other space environments and may be detectable by the new orbiting telescopes that indeed are able to cover not only the mid-infrared spectral range but also the far-infrared. This work supplies the reference spectra of the five nucleobases used by the terrestrial biochemistry in the mid-infrared and in the far-infrared with the purpose to facilitate the search and identification of these astrobiological and astrochemical relevant molecules in space. The mid-infrared spectra of all nucleobases were recorded at three different temperatures from −180 °C to nearly ambient temperature and at +250 °C. Furthermore, the molar extinction coefficients (ε) of all mid- and far-infrared bands were determined, as well as the integrated molar absorptivities (ψ). With the reported infrared spectra together with the ε and ψ values, it will be possible to identify qualitatively the nucleobases and estimate their relative abundance in space. [ABSTRACT FROM AUTHOR]

Alanine and other five proteinogeninc amino acids produced quite easily in exogenous and/or endogenous prebiotic processes, that is, valine, serine, proline, glutamic acid, and aspartic acid (Ala, Val, Ser, Pro, Glu, and Asp, respectively) were studied in the mid- and far-infrared spectral range. This work is an extension of the previous one where other proteinogenic amino acids glycine, isoleucine, phenylalanine, tyrosine, and tryptophan (Gly, Ile, Phe, Tyr, and Trp, respectively) were studied in the mid-infrared and in the far-infrared with the purpose to facilitate the search and identification of these astrobiological and astrochemical relevant molecules in space environments. The molar extinction coefficients (ɛ) of all mid- and far-infrared bands were determined as well as the integrated molar absorptivities (ψ). The mid-infrared spectra of Ala, Val, Ser, Pro, Glu, and Asp were recorded also at three different temperatures from −180°C to nearly ambient temperature and at 200°C. With the reported values of ɛ and ψ, it will be possible to estimate the relative abundance of these molecules in space environments. [ABSTRACT FROM AUTHOR]

A selection of five proteinogenic amino acids—glycine, isoleucine, phenylalanine, tyrosine, and tryptophan—were studied in the mid-infrared and in the far-infrared with the purpose to facilitate the search and identification of these astrobiologically and astrochemically relevant molecules in space environments. The molar extinction coefficients (ɛ) of all mid- and far-infrared bands were determined as well as the integrated molar absorptivities (ψ). The mid-infrared spectra of the five selected amino acids were recorded also at three different temperatures from -180°C to ambient temperature to +200°C. We measured the wavelength shift of the infrared bands caused by temperature; and for the most relevant or temperature-sensitive infrared bands, a series of linear equations were determined relating wavelength position with temperature. Such equations may provide estimates of the temperature of these molecules once detected in astrophysical objects; and with the reported values of ɛ and ψ, it will be possible to estimate the relative abundance of these molecules in space environments. [ABSTRACT FROM AUTHOR]

Boron carbide B4C or, which is the same, B12C3, was neutron-bombarded at four different doses, namely at 1.09, 2.19, 3.28 and 4.38 × 1016n cm−2. The radiation-damage was studied by FT-IR, ESR (Electron Spin Resonance) and by DSC (Differential Scanning Calorimetry). It is shown that both FT-IR and ESR are useful techniques to monitor the radiation-damage level introduced in B12C3, with the ESR characterized by a higher sensitivity level than FT-IR. Thermal annealing of the neutron-treated B12C3from room temperature to 630°C permits to measure the release of the stored Wigner energy which was found comprised between 0.55 meV/atom at the lowest neutron dose to 2.29 meV/atom at the highest neutron dose employed. The values of Wigner energy measured on B12C3were comparable to those measured on fullerenes and graphite flakes at the same dose level. However, the thermal annealing of neutron-treated B12C3does not lead to the complete restoration of the pristine chemical structure before irradiation. [ABSTRACT FROM AUTHOR]

C60and C70fullerenes were neutron-bombarded to an integral dose of 3.28×1016n cm−2. After the neutron treatment the trichloromethane soluble fraction was determined spectrophotometrically and C60insoluble fraction was found at 3.8% while the insoluble fraction of C7017.9%. The formation of the CHCl3insoluble fraction is due to polymerization and incipient amorphization of the neutron-bombarded fullerenes where C70appears more sensitive to radiation damage than C60. Raman spectroscopy was used for the characterization of the irradiated fullerenes as well as electron spin resonance (ESR) and electronic absorption spectroscopy on solid samples. Differential scanning calorimetry (DSC) to 630°C was employed for the determination of the Wigner energy of the neutron-damaged fullerenes. The results are consistent with a higher level of radiation damage reached by C70in comparison to C60at the same neutron dose. [ABSTRACT FROM AUTHOR]

Single-Wall Carbon Nanohorns (SWCNH) were ozonized with two different methodologies in batch and in continuous. The oxidation degree of SWCNH was determined by the FT-IR spectroscopy which is also able to detect the presence of secondary ozonide groups. The thermal treatment of the ozonized SWCNH at 350°C under N2caused the decomposition of the secondary ozonide groups as evidenced by FT-IR spectroscopy. Furthermore ozonized SWCNH were studied by differential scanning calorimetry (DSC). The typical exothermal decomposition of the ozonides was observed with DSC but at higher temperatures than usual and with an activation energy of 120 kJ/mol. Based on the decomposition heat released, about 4–5 secondary ozonide groups per each SWCNH were estimated. Fully ozonized SWCNH are easily and completely dispersible in distilled water giving a brown solution and lowering the pH to 5.9. Electronic absorption spectra of these solutions are reported. The water dispersions of ozonized SWCNH are able to reduce Ag+ions to silver nanoparticles but the resulting colloidal solution is unstable and flocculate. [ABSTRACT FROM PUBLISHER]

Ozonized C70fullerene known as C70ozopolymer or C70fullerene polyoxide was thermally decomposed in a Differential Scanning Calorimeter (DSC). The exothermal decomposition enthalpy was measured together with the activation energy for the thermal decomposition. The decomposition of C70ozopolymer was also studied with FT-IR spectroscopy showing that the thermal treatment at 350°C under N2causes the disappearance of the secondary ozonide groups and a series of the rearrangements of the oxygenated groups present in the compound. The reduction properties of C70ozopolymer were successfully assessed in the formation of silver nanoparticles from an acqueous solution of Ag+ions. [ABSTRACT FROM PUBLISHER]

The DSC (Differential Scanning Calorimetry) analysis of heavy ozonized C60fullerene (known also as “fullerene ozopolymer”), shows the exothermal decomposition of this compound with a peak at 158°C with a decomposition enthalpy ΔHdec≈ −322 kJ/mol and an activation energy for the decomposition E#= 71 kJ/mol. These experimental facts confirm the secondary ozonide/peroxidic and polymeric nature of fullerene ozopolymer originally suggested by the infrared spectroscopy analysis and solid state13C-NMR spectroscopy. It is also shown that the secondary ozonide group of fullerene ozopolymer can be reduced selectively by a treatment with hydrogen iodide. [ABSTRACT FROM AUTHOR]

The electronic absorption spectrum of single-walled carbon nanohorn (SWCNH) shows a relatively broad absorption peak at 256–259 nm when suspended in tetradecane and in decalin. The electronic absorption spectrum is also characterized by a series of small bands recalling the spectra of C60and C70fullerenes. Surprisingly, SWCNH shows a minimal solubility in 1,2,4-trichlorobenzene. SWCNH is also dissolved and oxidized in oleum (fuming sulphuric acid with 20% free SO3), displaying a radical cation band in the near infrared at 1045 nm. The addition of ozone to a suspension of SWCNH in oleum enhances its dissolution and the relative radical cation absorption band. [ABSTRACT FROM AUTHOR]

The FT-IR spectra of C76, C78and C84fullerenes were recorded in the temperature range between −180°C and +250°C. The purpose of the work is to provide reference infrared spectra for searching higher fullerene homologues in space after the recent and successful discovery of C60and C70in a series of different astrophysical objects. [ABSTRACT FROM AUTHOR]

Abstract: A series of non-proteinogenic amino acids, most of them found quite commonly in the meteorites known as carbonaceous chondrites, were subjected to solid state radiolysis in vacuum to a total radiation dose of 3.2 MGy corresponding to 23% of the total dose expected to be taken by organic molecules buried in asteroids and meteorites since the beginning of the solar system 4.6 x 109 years ago. The radiolyzed amino acids were studied by FT-IR spectroscopy, Differential Scanning Calorimetry (DSC) and by polarimety and Optical Rotatory Dispersion (ORD). It is shown that an important fraction of each amino acid is able to "survive" the massive dose of radiation, while the enantiomeric excess is partially preserved. Based on the results obtained, it is concluded that it is unsurprising to find amino acids even in enantiomeric excess in carbonaceous chondrites. [ABSTRACT FROM AUTHOR]

The radical anion spectra of C60 and C70 can be easily generated and studied in primary aliphatic amines. In these conditions the C60 _• and C70 _• species are accompanied by the dianions C60 2− and C70 2−. In the near infrared region the electronic transitions at 1075, 1058 and 991 nm were assigned to C60 _• while those at 1020–1030 nm and at 933 nm were assigned to the fullerene dianion C60 2−. The electronic transition of C70 _• occurs at 1370 nm and that of C60 2− at 1170 nm, but in primary aliphatic amines C70 also display a broad absorption band at 814–820 nm with other features certainly due to a specific interaction of the amine with C70. The behavior of C60 was studied with primary aromatic amines, but no interaction was found. Furthermore, solutions of C60 and C70 were studied with the secondary amine dioctylamine and with the tertiary amines triethylamine and N,N,N',N'-tetramethylethylenediamine (TMEDA). FT-IR spectra of selected fullerene-amine adducts were reported. [ABSTRACT FROM PUBLISHER]

The integrated molar absorptivity (Ψ) and the molar extinction coefficient (ε) of each infrared transition of the hydrogenated fullerenes (known as fulleranes) C60H36, C70H38 and a mixture of fulleranes generally referred as 77% of C60Hx and 22% C70Hy with x ≈ y > 30 were determined. These data are useful for the search, identification and quantitative determination of fulleranes in space after the recent discovery that their parent molecules C60 and C70 are present in certain planetary nebulae and in the interstellar medium. It is shown that the C-H stretching band of fulleranes C60H36, C70H38 and their mixture at about 2905 and 2820 cm−1 are the most useful for the identification of these molecules because their Ψ and ε values are unique in terms of strength overcoming by far the typical Ψ and ε values of reference molecules like adamantane and docosane as well as typical ε literature data for aliphatic molecules. [ABSTRACT FROM AUTHOR]

The radical cation of the fullerene series C60, C70,C76, C78 and C84 were generated in oleum (fuming sulphuric acid with 30% free SO3) and analyzed by electronic absorption spectroscopy. A general agreement was found between the fullerenes radical cation spectra generated in oleum and those described in the literature and produced in other conditions. An attempt to correlate the radical cation transition of C60, C70, C76, C78 and C84 in oleum with their ionization potential was proposed. [ABSTRACT FROM AUTHOR]

A series of fulleranes, namely C60H36, C70H38, C60H18 and a mixture of hydrogenated fullerenes composed by 77% C60Hx and 22% C70Hy, were dissolved in oleum (fuming sulfuric acid) in order to record the radical cation spectra of these molecules. Surprisingly, it was found that the fulleranes spectra in oleum corresponded to the radical cation spectra of pristine C60 and C70 fullerenes. Therefore, it was concluded that the fulleranes in a high ionizing and oxidizing medium such as oleum are dehydrogenated and oxidized to C60 +• and C70 +•. The prolonged contact with oleum leads to multiple sulfonation of the radical cations. [ABSTRACT FROM AUTHOR]

ABSTRACT The infrared spectra, as well as the integrated molar absorptivity (Ψ) and the molar extinction coefficient (ɛ) of each infrared transition of the hydrogenated fullerenes (known as fulleranes) C60H36, C60H18 and C70H38, and a mixture of fulleranes generally referred to as 77 per cent of C60Hx and 22 per cent C70Hy with x≈ y > 30, are presented and discussed. These data are useful for the search, identification and quantitative determination of fulleranes in space after the recent discovery that their parent molecules, C60 and C70, are more abundant in space than initially thought, being present in a variety of H-rich circumstellar environments such as planetary nebulae and only mild H-deficient R Coronae Borealis stars, and in the interstellar medium. It is shown that the C-H stretching band of the fulleranes C60H36, C60H18 and C70H38, and their mixture may be most useful for the identification of these molecules because their Ψ and ɛ values are unique in terms of strength, overcoming by far the typical Ψ and ɛ values of reference molecules such as adamantane and docosane, as well as typical ɛ literature data for aliphatic molecules. In contrast to the rather simple infrared spectra of C60H36 and C60H38, the infrared spectra of two C60H18 isomers are reported as characterized by a rich number of bands which may allow an easier identification than the higher homologues. The dependence of the infrared bands of fulleranes on temperature was studied over a wide range of temperatures (from −180°C to +250°C) and extrapolated to 0 K. [ABSTRACT FROM AUTHOR]

The molar extinction coefficients, known also as molar absorptivity ɛ, of C60 and C70 fullerenes infrared absorption spectra were determined at room temperature on samples embedded in KBr pellets. Furthermore, the integrated molar absorptivity Ψ of each absorption infrared band either of C60 and of C70 was measured and reported together with the relative intensity of the infrared absorption bands. These results can be useful in the quantitative determination of C60 and C70 fullerenes in space after the recent discovery that these molecules are present around the young planetary nebula Tc1. [ABSTRACT FROM PUBLISHER]

ABSTRACT We have obtained high-resolution optical spectroscopy of 10 reddened O-type stars with Ultraviolet and Visual Echelle Spectrograph at Very Large Telescope to search for interstellar bands of the naphthalene cation (C10H8+) in the intervening clouds. No absorption features were detected near the laboratory strongest band of this cation at 6707 Å except for star HD 125241 (O9 I). Additional bands in the optical spectrum of this star appear to be consistent with other transitions of this cation. Under the assumption that the bands are caused by naphthalene cations, we derive a column density = (1.2 ± 0.3) × 10 13 cm−2 similar to the column density claimed in the Perseus complex star Cernis 52. The strength ratio of the two prominent diffuse interstellar bands at 5780 and 5797 Å suggests the presence of a σ-type cloud in the line of sight of HD 125241. [ABSTRACT FROM AUTHOR]

The Scholl reaction was adopted to synthesize the very large polycyclic aromatic hydrocarbons (VLPAHs) hexabenzocoronene (HBC), quaterrylene and dicoronylene as well as their nonalternant isomers. These molecules can be considered subsections of a graphene sheet since the radial diameter of HBC is 13.5 Å and the length of both quaterrylene and dicoronylene is about 17.9 Å. Improved synthetic procedures of synthesis are presented, and the resulting VLPAHs were isolated and recognized from their characteristic electronic absorption spectra. The precursor PAHs used in the Scholl's synthesis where studied by differential scanning calorimetry (DSC), and the thermal behavior of the resulting VLPAHs was studied by thermogravimetric analysis and differential thermal analysis (TGA-DTA). The VLPAHs hexabenzocoronene (HBC), quaterrylene and dicoronylene show a trend to carbonization (growth of the laminar molecules into stacked and large graphene sheets) when heated slowly to high temperature in a nitrogen atmosphere. [ABSTRACT FROM AUTHOR]

ABSTRACT The detection of C60 and C70 fullerenes in young planetary nebulae and in reflection nebulae suggests that these molecules are more common in certain astrophysical environments than previously thought. The dependence on temperature of the positions and widths of the infrared bands of the C60 and C70 fullerenes is needed for a firm qualitative detection of these molecules in space. Furthermore, the integrated molar absorptivity Ψ (in km mol−1) of each infrared absorption band is required for a quantitative determination of the abundance of C60 and C70 in space. In this paper, we report on the temperature dependence of the wavelength shift and integrated molar absorptivity of the infrared bands of the C60 and C70 fullerenes. The measurements have been made in a KBr matrix in the temperature range between −180°C and +250°C. The experimental data have been extrapolated to derive both the infrared band shift and the integrated molar absorptivity of the C60 and C70 fullerenes at absolute zero temperature. [ABSTRACT FROM AUTHOR]

Interstellar absorption lines up to in the band and up to in the band of the C system are detected toward star Cernis 52 (BD +31°640) in the Perseus molecular complex. The star lies in a reddened line of sight where various experiments have detected anomalous microwave emission spatially correlated with dust thermal emission. The inferred total C column density of is well correlated with that of CH, as expected from theoretical models, and is among the highest reported for translucent clouds with similar extinction. The observed rotational C lines constrain the gas kinetic temperature T and the density of the intervening cloud to K and , respectively. This is the first determination of the gas kinetic temperature and particle density of a cloud with known anomalous microwave emission. [ABSTRACT FROM AUTHOR]

ABSTRACT Amino acids in Solar system bodies may have played a key role in the chemistry that led to the origin of life on Earth. We present laboratory studies testing the stability of amino acids against high energy radiation. All the 20 chiral amino acids in the levo form found in the proteins of the current terrestrial biochemistry were irradiated in the solid state with γ-radiation to a dose of 3.2 MGy, which is the dose equivalent to that produced by radionuclide decay in comets and asteroids in 1.05 × 109 yr. For each amino acid the radiolysis degree and the radioracemization degree were measured by differential scanning calorimetry and by optical rotatory dispersion spectroscopy. From these measurements, a radiolysis rate constant kdsc and a radioracemization rate constant krac were determined for each amino acid and extrapolated to a dose of 14 MGy, which corresponds to the expected total dose delivered by natural radionuclide decay to all the organic molecules present in comets and asteroids in 4.6 × 109 yr, the age of the Solar system. It is shown that all the amino acids studied can survive a radiation dose of 14 MGy, although certain fractions of them are lost as a result of radiolytic processes. Similarly, the radioracemization process accompanying the radiolysis does not extinguish the initial enantiomeric enrichment. Knowledge of the radiolysis and radioracemization rate constants may permit the calculation of the original concentrations of the amino acids at the time of the formation of the Solar system, starting from the concentration found today in carbonaceous chondrites. For some amino acids the concentration in the pre-solar nebula could have been up to 6 times higher than that currently observed in meteorites. The preservation of an original enatiomeric excess is also expected. This study adds experimental support to the suggestion that amino acids were formed in the interstellar medium and in chiral excess and then were incorporated into comets and asteroids at the epoch of Solar system formation. [ABSTRACT FROM AUTHOR]

The FT-IR spectra of the fullerenes C60 and C70 have been recorded in the temperature range between 523 K (+250°C) and 93 K (-180°C). As a general rule, it has been observed a shift of the infrared absorption bands toward higher frequencies at lower temperatures. As expected, at 93 K the infrared spectra appear better resolved with sharper absorption bands and higher intensity than the same bands measured at higher temperature. All the infrared spectra of the present study have been made on samples embedded in KBr matrix and all data were extrapolated to 0 K. These spectral data at extremely low temperatures are of paramount importance for astrochemical search of these molecules in space. By comparing the gas phase spectra of both C60 and C70 fullerenes extrapolated to 0 K with the data taken in KBr matrix, the gas phase spectral bands were found systematically shifted 5-10 cm-1 toward higher frequencies than the same bands recorded in KBr. Similarly, the matrix effect is appreciable also when the spectral data taken in KBr are extrapolated to >1000 K. In such case the band position of C60 and C70 fullerenes in the gas phase are shifted to lower frequencies than the extrapolation data taken in KBr matrix. [ABSTRACT FROM AUTHOR]

Polynomial behaviour of the Wiener index for infinite chemical graphs is subject here to a generalisation to structures with topological dimensionality dT>1. This allows a pure topological analysis of relative chemical stability of graphite lattice portions and fullerene fragments (nanocones) built around a pentagonal face. The Wiener index of the graph acts as a lattice topological potential subject to a minimum principle that is able to discriminate topological structures made of hexagons with different connectivity. A new indicator of graph topological efficiency has been applied in the infinite lattice limit to allow a complete ranking of graph chemical stability. A certain grade of reactivity of the pentagonal ring at the centre of nanocones is also predicted. Our considerations are mainly performed in the dual topological space. [ABSTRACT FROM AUTHOR]

A commercially available hydrogenated mixture of fullerenes (HMF) composed of 77% C60Hx and 22% C70Hx has been analyzed by liquid chromatographic analysis (HPLC), electronic absorption, FT-IR spectroscopy, solubility and by thermal analysis (TGA). The results confirm that the HMF is composed by a mixture of C60Hx and C70Hx with a high degree of hydrogenation. The hydrogen content of the HMF was found 6.12% by combustion elemental analysis, suggesting that hydrogenated fullerenes are mixed with hydrogenated fullerene fragments derived from the cage breakdown due to the forcing conditions used in the synthesis (high pressure and high temperature hydrogenation). The HMF is stable in air for a relatively long time of exposure. Under N2, it starts to decompose at 478°C. The maximum decomposition rate under N2 occurs at 522°C. An attempt was made to resolve the C-H stretching band of HMF by recording the FT-IR spectrum at -180°C. [ABSTRACT FROM AUTHOR]

C60 fullerene can be easily hydrogenated in aromatic solvent under mild conditions with aqueous hydrogen iodide (HI). The resulting black product has the molecular formula C60H24•2I2 on the basis of the FT-IR spectroscopy and of the thermogravimetric analysis. When this compound is heated under N2 it releases I2 and HI producing exclusively C60H18, which was recognized with FT-IR spectroscopy. [ABSTRACT FROM AUTHOR]

Fulleranes, the hydrogenated fullerenes C60H36 and C60D36 have been synthesized in n-hexane where they show an absorption maximum at 217 nm in their electronic absorption spectra with molar extinction coefficients and 16 480 L cm−1 mol−1, respectively, which correspond to absorption cross-sections of order 6500 Mbarn, about 10 times higher than for C60. We find that the absorption curves measured for these two fulleranes fit well the wavelength, width and shape of the ultraviolet (UV) bump (217 nm) in the extinction curve of the diffuse interstellar medium. If present in the interstellar medium these fulleranes would contribute significantly to the bump extinction, although interstellar carbon budget considerations indicate that C60H36 cannot be the only contributor. The photolysis of fulleranes with monochromatic light at 245 nm causes a shift of the absorption maximum from 217 nm to longer wavelengths. This band shift of the absorption maximum has already been observed in the photolysis or in the thermal processing of hydrogenated carbon dust. The band shift is due to the release of molecular hydrogen, a process which causes the aromatization of the carbon dust. C60H36 and C60D36 are photolyzed at a rate while . This implies an isotope effect so that C60H36 is photolyzed 1.08 times faster than C60D36. In the interstellar medium, this implies a deuterium enrichment of the hydrogenated interstellar carbon dust. The presence of a measurable isotope effect suggests that the photolysis of C60H36 and C60D36 involves the rupture of the C-H and C-D bond with release of H2. C60H36 releases completely hydrogen when heated to 630 °C under inert atmosphere producing back C60 as shown by FT-IR spectroscopy. Thus in the interstellar medium an equilibrium should occur between the hydrogenation of C60 with atomic hydrogen and the emission of molecular hydrogen because of the action of UV photons or thermal processing. Interstellar fullerenes and interstellar carbon dust containing fullerenes and fullerene-like structures should play a key role in the formation of molecular hydrogen starting from atomic hydrogen and as carriers of the UV bump of the interstellar extinction curve. [ABSTRACT FROM AUTHOR]

Fulleranes, the hydrogenated fullerenes C60H36 and C60D36 have been synthesized in n-hexane where they show an absorption maximum at 217 nm in their electronic absorption spectra with molar extinction coefficients and 16 480 L cm−1 mol−1, respectively, which correspond to absorption cross-sections of order 6500 Mbarn, about 10 times higher than for C60. We find that the absorption curves measured for these two fulleranes fit well the wavelength, width and shape of the ultraviolet (UV) bump (217 nm) in the extinction curve of the diffuse interstellar medium. If present in the interstellar medium these fulleranes would contribute significantly to the bump extinction, although interstellar carbon budget considerations indicate that C60H36 cannot be the only contributor. The photolysis of fulleranes with monochromatic light at 245 nm causes a shift of the absorption maximum from 217 nm to longer wavelengths. This band shift of the absorption maximum has already been observed in the photolysis or in the thermal processing of hydrogenated carbon dust. The band shift is due to the release of molecular hydrogen, a process which causes the aromatization of the carbon dust. C60H36 and C60D36 are photolyzed at a rate while . This implies an isotope effect so that C60H36 is photolyzed 1.08 times faster than C60D36. In the interstellar medium, this implies a deuterium enrichment of the hydrogenated interstellar carbon dust. The presence of a measurable isotope effect suggests that the photolysis of C60H36 and C60D36 involves the rupture of the C-H and C-D bond with release of H2. C60H36 releases completely hydrogen when heated to 630 °C under inert atmosphere producing back C60 as shown by FT-IR spectroscopy. Thus in the interstellar medium an equilibrium should occur between the hydrogenation of C60 with atomic hydrogen and the emission of molecular hydrogen because of the action of UV photons or thermal processing. Interstellar fullerenes and interstellar carbon dust containing fullerenes and fullerene-like structures should play a key role in the formation of molecular hydrogen starting from atomic hydrogen and as carriers of the UV bump of the interstellar extinction curve. [ABSTRACT FROM AUTHOR]

Perdeuterofullerane, C60D36 was synthesized in toluene solution from DCl and Zn. The FT-IR spectrum of C60D36 was compared with that of C60H36, and the C-H stretching and bending shift due to deuteration was measured so that Ω H/ Ω D = 1.36. The thermal stability of C60D36 was studied under N2 by thermogravimetric and differential thermal analysis. It has been found that the substitution of hydrogen with deuterium in fullerene leads to a significant increase in thermal stability which was attributed to isotope effect. In particular, the onset of decomposition of C60H36 occurred at 412°C in comparison to 465°C measured on C60D36. The maximum decomposition rate of C60H36 was found at 501°C and was shifted to 549°C in C60D36. Perdeuterofullerane was found much more stable also to air oxidation. It oxidized slowly when exposed to air and some days were needed to reach a degree of oxidation, which was reached in 1 hour by C60H36. [ABSTRACT FROM AUTHOR]

The hydrogenated C70 fullerenes C70H38 and C70D38 have been photolyzed at 245 nm under Ar or He flow. The photolysis rate constant have been measured: k = 1.54×10-3 s-1 for C70H38, and the photolysis of C70D38 occurs at a rate of 1.17×10-3 s-1. A remarkable isotope effect in the photolysis of the two molecules has been determined kH/kD = 1.32. The photolysis mechanism and products of C70H38 and C70D38 have been discussed and, based on the isotope effect, the rate determining step involves, as for other fulleranes, the activation of the C-H and C-D bond. The UV photons cause the dehydrogenation of C70H38 and C70D38 and their oligomerization. In an astrochemical context the photolysis reaction of C70H38 should produce back C70 with release of molecular hydrogen. The role of fulleranes and hydrogenated carbon with fullerene-like structure in space has been briefly discussed. C70H38 thermally treated at 600°C under N2 releases H2 forming back C70, which was easily recognized from its characteristic FT-IR spectrum. The reaction is not fully reversible, and carbonaceous matter is formed as secondary product. The molar extinction coefficient of C70H38 and C70D38 has been determined in n-hexane at 214 nm, the maximum of absorption of these two molecules; ε214 = 6300 L cm-1 mol-1 for the former and ε214 = 5800 L cm-1 mol-1 for the deuterated fullerane. [ABSTRACT FROM AUTHOR]

Fullerane C60H18 and its deuterated analogous C60D18 were synthesized in n-hexane solution by a reduction reaction of C60 under the action of HCl or DCl on Zn dust. The resulting solutions were subjected to UV irradiation at 245 nm from a low pressure mercury lamp under He. It was found that at 212 nm the photolysis rate constant of C60H18 molecule Hk212 = 8.68 × 10-4 s-1 was significantly higher than that of its deuterated analogous C60D18: Dk212 = 5.93 × 10-4 s-1. Similarly, at 256 nm it was confirmed the result that C60D18 was photolyzed more slowly than C60H18. Also in this case, Hk256 = 6.83 × 10-4 s-1 is significantly higher than that of its deuterated analogous C60D18: Dk212 = 3.74 × 10-4 s-1. Kinetic isotope effect involving the C-H and C-D bond activation has been advocated to explain the differences in photodecomposition speed of C60H18 in comparison to C60D18. On the basis of solubility in alkanes and unique electronic absorption spectrum C60H18 with C3ν symmetry prepared under high hydrogen pressure can be easily distinguished from the C60H18 and its deuterated analogous C60D18 synthesized in n-hexane from Zn/HCl or Zn/DCl. The C3ν - C60H18 displayed also a different evolution of the electronic absorption spectrum under photolysis in comparison to C60H18 and its deuterated analogous C60D18. The pseudofirst rate constant of C3ν -C60H18 is k217 = 4.04 × 10-4 s-1 and k255 = 2.25 × 10-4 s-1. [ABSTRACT FROM AUTHOR]

Perdeutero[70]fullerane, C70D38 and the hydrogenated analogous C70H38 have been synthesized using nascent deuterium or hydrogen generated by the action of DCl or HCl on Zn dust in toluene or benzene solvents. The FT-IR spectra of C70D38 and C70H38 have been studied. A better oxidation stability of C70D38 has been observed by FT-IR spectroscopy in comparison to that of C70H38. Similarly, thermogravimetric analysis (TGA) and differential thermal analysis (DTA) have revealed a better thermal stability of the deuterated molecule in comparison to its hydrogenated analogous. The results have been interpreted in terms of isotope effect. Oxidized fulleranes are soluble in concentrated sulphuric acid where they undergo a partial elimination reaction producing fullerenes with a lower degree of hydrogen content. [ABSTRACT FROM AUTHOR]

The stability of C60 and C70 fullerenes in the interstellar medium deposited on dust surface or embedded in meteorites and comets has been simulated with γ irradiation and with He+ ion bombardment. It is shown by vibrational spectroscopy that a γ radiation dose of 2.6 MGy (1 Gy = 1 joule absorbed energy per kilogram) causes partial oligomerization of both C60 and C70 fullerenes. Oligomers are made by fullerene cages chemically connected each other which can yield back free fullerenes by a thermal treatment. The amount of irreversibly polymerized fullerenes caused by 2.6 MGy as deduced as the toluene insoluble fraction has been determined as 1.7 and 15 per cent by weight, respectively, for C60 and C70 fullerene. The radiation dose generated by radionuclides decay and expected to be delivered to fullerenes buried at a depth of more than 20 m in comets and meteorites is about 3 MGy per 109 yr. Since fullerenes are by far resistant to such radiation dose they can survive for at least some billion years inside comets and meteorites and in fact have been detected inside certain carbonaceous chondrites. On the other hand, the direct exposure of fullerenes to cosmic rays for instance when they are adsorbed or deposited on the surface of carbon dust corresponds to the delivery of a radiation dose comprised between 30 and 65 MGy per 109 yr. Experimental bombardment of both C60 and C70 fullerenes for instance with He+ ions has shown that the complete amorphization occurs at about 250 MGy. Thus in ∼4 Gyr exposure to cosmic rays it is expected a complete amorphization. [ABSTRACT FROM AUTHOR]

According to semiempirical models, photoabsorption by fullerenes (single and multishell) could explain the shape, width and peak energy of the most prominent feature of the interstellar absorption, the UV bump at 2175 Å. Other weaker transitions are predicted in the optical and near-infrared providing a potential explanation for diffuse interstellar bands. In particular, we find that several fullerenes could contribute to the well known strong DIB at 4430 Å. Comparing cross sections and available data for this DIB and the UV bump we estimate a density of fullerenes in the diffuse interstellar medium of 0.1–0.2 ppm. These molecules could then be a major reservoir for interstellar carbon. We also study the rotation rates and electric dipole emission of hydrogenated icosahedral fullerenes. We investigate these molecules as potential carriers of the anomalous (dust-correlated) microwave emission recently detected by several cosmic microwave background experiments. [ABSTRACT FROM PUBLISHER]

We study the rotation rates and electric dipole emission of hydrogenated icosahedral fullerenes under the physical conditions of the dark cloud (DC) LDN 1622. The abundance of fullerenes is estimated by fitting theoretical photoabsorption spectra to the characteristics of the ultraviolet (UV) bump extinction in DCs. The UV bump appears to be well reproduced by a mixture of fullerenes following a size-distribution power law, which gives progressively lower abundances as the radius of the fullerene increases. We infer abundances of the order of for C60. A significant fraction of these molecules are expected to be hydrogenated. We compute the electric dipole rotational emission from these fullerene hydrides, taking into account rotational excitation and damping processes. The recent detection of anomalous microwave emission (5–60 GHz) in LDN 1622 by Casassus et al. can be explained as the result of electric dipole radiation from hydrogenated fullerenes. The bulk of the emission (10–30 GHz) appears to be associated with 60–80 carbon atom fulleranes with a degree of hydrogenation of C:H ≈ 3:1. A small contribution (∼10 per cent) of these molecules residing in the surrounding cold neutral medium and/or photodissociation region of the cloud is required to fit the high-frequency tail (40–60 GHz) of the emission. [ABSTRACT FROM AUTHOR]