We present 10 new Spitzer detections of fullerenes in Magellanic Cloud Planetary Nebulae, including the first extragalactic detections of the C 70 molecule. These new fullerene detections together with the most recent laboratory data permit us to report an accurate determination of the C 60 and C 70 abundances in space. Also, we report evidence for the possible detection of planar C 24 in some of our fullerene sources, as indicated by the detection of very unusual emission features coincident with the strongest transitions of this molecule at ∼6.6, 9.8, and 20 μm. The infrared spectra display a complex mix of aliphatic and aromatic species such as hydrogenated amorphous carbon grains (HACs), polycyclic aromatic hydrocarbon clusters, fullerenes, and small dehydrogenated carbon clusters (possible planar C 24 ). The coexistence of such a variety of molecular species supports the idea that fullerenes are formed from the decomposition of HACs. We propose that fullerenes are formed from the destruction of HACs, possibly as a consequence of shocks driven by the fast stellar winds, which can sometimes be very strong in transition sources and young planetary nebulae (PNe). This is supported by the fact that many of our fullerene-detected PNe show altered [Ne iii]/[Ne ii] ratios suggestive of shocks as well as P-Cygni profiles in their UV lines indicative of recently enhanced mass loss.

We report high resolution spectroscopy of the moderately reddened (A V =3) early type star Cernis 52 located in a region of the Perseus molecular cloud complex with anomalous microwave emission. In addition to the presence of the most common diffuse interstellar bands (DIBs) we detect two new interstellar or circumstellar bands coincident to within 0.01% in wavelength with the two strongest bands of the naphthalene cation (C 10 H + 8 ) as measured in gas-phase laboratory spectroscopy at low temperatures and find marginal evidence for the third strongest band. Assuming these features are caused by the naphthalene cation, from the measured intensity and available oscillator strengths we find that 0.008 % of the carbon in the cloud could be in the form of this molecule. We expect hydrogen additions to cause hydronaphthalene cations to be abundant in the cloud and to contribute via electric dipole radiation to the anomalous microwave emission. The identification of new interstellar features consistent with transitions of the simplest polycyclic aromatic hydrocarbon adds support to the hypothesis that this type of molecules are the carriers of both diffuse interstellar bands and anomalous microwave emission.

The detection of C 60 and C 70 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 C 60 and C 70 fullerenes is needed for a firm qualitative detection of these molecules in space. Furthermore, the integrated molar absorptivity (in km mol −1 ) of each infrared absorption band is required for a quantitative determination of the abundance of C 60 and C 70 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 C 60 and C 70 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 C 60 and C 70 fullerenes at absolute zero temperature.

We show that photoabsorption by fullerenes and buckyonions (multishell fullerenes) explain the shape, width, and peak energy of the most prominent feature of interstellar absorption, the UV bump at 2175 . The predicted A optical and near-infrared transitions for these molecules also offer a potential explanation for the long-standing problem of the identity of the diffuse interstellar bands. The implied ubiquitous distribution of fullerenes may also account for the anomalous galactic microwave emission detected by cosmic microwave background experiments. Comparing theoretical cross sections and astronomical data, we estimate a density of fullerenes in the diffuse interstellar medium of 0.1-0.2 parts per million, consistent with the findings in meteorites. Fullerenebased molecules appear to be a major carbon reservoir in the interstellar medium.

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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.

We report the discovery of a new broad interstellar (or circumstellar) band at 7088.8 ± 2.0 Å coincident to within the measurement uncertainties with the strongest band of the anthracene cation (C 14 H 10 + ) as measured in gas-phase laboratory spectroscopy at low temperatures. The band is detected in the line of sight of star Cernis 52, a likely member of the very young star cluster IC 348, and is probably associated with cold absorbing material in an intervening molecular cloud of the Perseus star-forming region where various experiments have recently detected anomalous microwave emission. From the measured intensity and available oscillator strength we find a column density of N an + = 1.1(±0.4) × 10 13 cm −2 implying that ∼0.008 per cent of the carbon in the cloud could be in the form of C 14 H 10 + . A similar abundance has been recently claimed for the naphthalene cation in this cloud. This is the first location outside the Solar system where specific polycyclic aromatic hydrocarbons (PAHs) are identified. We report observations of interstellar lines of CH and CH + that support a rather high column density for these species and for molecular hydrogen. The strength ratio of the two prominent diffuse interstellar bands at 5780 and 5797 Å suggests the presence of a 'zeta'-type cloud in the line of sight (consistent with steep far-ultraviolet extinction and high molecular content). The presence of PAH cations and other related hydrogenated carbon molecules which are likely to occur in this type of clouds reinforces the suggestion that electric dipole radiation from fast-spinning PAHs is responsible of the anomalous microwave emission detected towards Perseus.

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.