Long carbon chain molecules in circumstellar shells

An intrinsic source of reddening in the cataclysmic variable SS Cygni

“…-Some studies (Iglesias-Groth 2004) demonstrate that fullerenes and buckyonions are the best candidates for explaining the shape, width and peak energy of the most prominent feature of the 2175 Å bump. -Other studies (Kuznetsov et al 1994;Ugarte 1995;Kroto et al 1987;Kroto 1997;Draine 2009) demonstrate that the formation of fullerenes and buckyonions is confirmed both in laboratory and in circumstellar envelopes of evolved stars and other astrophysical environments. -The very high obtained significance value of 99.95%, confirming the hypothesis for having E(B − V) > 0.04 mag, points out the necessity of investigating the reason of this variation taking into account the fullerenes hypothesis rather than that of the hydrogen column density.…”

“…It has been verified in laboratory experiments that an excess of carbon or oxygen content in a gas mixture inhibits diamond formation, which can be precursors of fullerene growth (Ugarte 1995). Moreover Kroto et al (1987) showed that in complex environments, high temperatures favor the formation of carbon/carbon bonds relative to carbon/hydrogen bonds because of the large difference in bond energies.…”

“…(Kuznetsov et al 1994;Ugarte 1995) and in the circumstellar envelopes of evolved stars and other astrophysical environments (see, e.g., Kroto et al 1987;Kroto 1997;and Draine 2009). It is therefore reasonable to suggest that fullerenes and buckyonions form and destroy inside the SS Cyg system during quiescence, thus contributing to the observed effect of a variable reddening.…”

Reactions of Gas-Phase Atomic Hydrogen with Chemisorbed Hydrogen on a Graphite Surface

“…[23][24][25] Since atomic hydrogen is by far the most abundant gaseous species in the interstellar medium at extreme temperatures (10 K), the problem of studying rates and mechanisms of the H(g)/ C(gr) reaction is then both interesting and important in understanding some astrophysical phenomena, such as the infrared emission of the interstellar clouds. 18,26 Therefore, the information on the amount of reaction energy deposited in the various motions of the nascent hydrogen molecule, especially its vibrational population distribution, should be particularly useful in understanding the infrared emission.…”

Terrestrial and Extraterrestrial Fullerenes

“…The most widely held view is that interstellar fullerenes formed initially in atmospheres of carbon-rich, hydrogen-poor stars whence they are delivered by strong stellar winds to interstellar media. Possible syntheses include carbon condensation, [1,[38][39][40][41][42] but also hydrogenation, [25][26][27][28][29][30] pyrolysis of gaseous molecules, [43] and decomposition of hydrogenated amorphous carbon. [44] Unfortunately, extensive experimental evidence shows that many other forms of elemental carbon are likely to form alongside fullerenes and it is still not understood which of these will be the most abundant in any of the relevant astrochemical environments.…”