In interstellar media

In the conventional view, both structures [1 and 2, A = C] are energetically almost perfectly degenerate, allowing virtually free rotation of the moiety, but the Cj form is about 1 kcal mor higher in energy. But why has CHj not been observed in interstellar media, and why is its characterization by infrared spectroscopy so difficult The only measurable experimental quantity, the dissociation energy 298 [42.5 kcal mor Equation 4], " shows that the methonium ion is quite... 

One of the incentives for studying transition states including angular momentum comes from molecular astrophysics. Conditions prevailing in interstellar media are such that very clean rotational effects are observed. Many reviews exist describing molecular environments in interstellar media, as well as their chemistry [81,82]. 

PAHs are recognized as cosmochemically important molecules, because they are abundantly detected in interstellar media, carbonaceous chondrites, and interplanetary dust particles. Although FTT reactions [42], the pyrolysis of hydrocarbons such as tlie polymerization of acetylene [138], and ion-molecule reactions [148] liave been accepted as responsible for tlie PAH genesis, the shock process discussed in the present study can be suggested as a strong candidate for PAH formation. Most species of PAHs detected in meteorites and interplanetaiy dust... 

Advances in Gas Phase Ion Chemistry is different from other ion chemistry series in that it focuses on reviews of the author s own work rather than give a generai review of the research area. This allows for presentation of some current work in a timely fashion which marks the unique nature of this series. Emphasis is placed on gas phase ion chemistry in its broadest sense to include ion neutral, ion electron, and ion-ion reactions. These reaction processes span the various disciplines of chemistry and include some of those in physics. Within this scope, both experimental and theoretical contributions are included which deal with a wide variety of areas ranging from fundamental interactions to applications in real media such as Interstellar gas clouds and pleismas used in the etching of semiconductors. The authors are scientists who are leaders in their fields and the series will therefore provide an up-to-date analysis of topics of current importance. This series is suitable for researchers and graduate students working in ion chemistry and related fields and will be an invaluable reference for years to come. The contributions to the series embody the wealth of molecular information that can be obtained by studying chemical reactions between ions, electrons and neutrals in the gas phase. 

In this chapter, we will review the characteristics of thermonuclear processing in the three environments we have identified (i) intermediate-mass stars (ii) massive stars and type II supemovae and (iii) type la supemovae. This will be followed by a brief discussion of galactic chemical evolution, which illustrates how the contributions from each of these environments are first introduced into the interstellar media of galaxies. Reviews of nucleosynthesis processes include those by Arnett (1995), Trimble (1975), Truran (1984), Wallerstein et al. (1997), and Woosley et al. (2002). An overview of galactic chemical evolution is presented by Tinsley (1980). 

C4H2 isomers are of great interest to astronomers because some of these molecules occur in the atmospheres of Titan [74] (and references therein), Jupiter [75] (and references therein), possibly Pluto [76] in a comet [77], and in circumstellar and interstellar media [42,78-80]. Quantum chemical treatments of the 18 possible constructs, which included branched open constructs, produced 10 molecules of which four were open and six were cyclical. All have singlet ground states. Several investigators have synthesized 4Ol(s) in the gas phase and in solvents. Goldberg et al. [81] have synthesized 4O2(s) in the gas phase. 

In the cosmos, however, carbon onions possibly exist. Soon after their discovery they have already been discussed as a potential reason for an up to then not interpretable absorption at 217.5 nm in the spectrum of interstellar space. The absorption spectrum of carbon onions closely resembles that of interstellar dust indeed. A red shift is observed on the occasion, yet this may be explained by the measurements being made in different media (water or vacuum, respectively Section 4.4.1.3). 

This way, all the ab initio results presented here, that we will interpret essentially within the viewpoint of chemistry in interstellar clouds, can also be used, mutatis mutandis, to investigate other astrophysical media such as comets or planetary atmospheres. 

The science involved is concerned with the electromagnetic phenomena in ionized media encountered in interstellar space, in stars, and above the atmosphere. Because these ionized materials are... 

Since the discovery of Cgo, elongated and elliptical cages of 70 and 80 carbon atoms have also been discovered. These molecules, called fullerenes as a group, have been proposed to exist in such exotic places as stars and interstellar media and have been observed in such mundane places as deposits of chimney soot. 

One of the most exciting applications since the 1970s has been the observation of microwave (rotational) spectra of interstellar molecules. Common species such as formaldehyde, ammonia and methylamine and more exotic species such as HCO and H—CC-C=C—CN have been detected in various interstellar media. The experimental technique differs substantially from that outlined in Figures 1 and 2. In this case the interstellar molecular spectra are detected by collecting microwave emissions from interstellar space with large radio telescopes equipped with sensitive... 

Mixtures of fulleranes produced by hydrogenation of solid C60 films under atomic H flux have revealed spectral features that bear striking similarity to those observed in the diffuse interstellar medium, both in the far IR and in the UV spectral windows. Of course, one must be cautious not to overextend the interpretation of laboratory data, for a number of reasons firstly, because electron spectroscopy, the experimental technique used in these studies, differs in several important aspects from the spectroscopic methods employed in observational astronomy, and secondly, because of the specifics of specimen preparation and environmental conditions. In this regard, there is a need to explore the stability of fulleranes to energetic and corpuscular radiation (Cataldo et al. 2009). Nonetheless, our findings lend support to the suggestion of fulleranes as candidates for unidentified emission and absorption features of interstellar and circumstellar media. Whether or not they exist in sufficient abundance is still unclear however, their spectral features make them undoubtedly an ideal model system for laboratory studies of these fascinating astrophysical phenomena. 

The 0( D) atom is a mctastablc sj)ccics vit,h a radiative lifetime of about 150 s. This species, with the ground 0( P) state of atomic oxygen, is an important constituent of several dilute media, such as the interstellar medium and the upper atmosphere. The rate constants of 0( D) 4 Ho, CH4, H2O and N2O reactions is much larger than for O( P) with the same species. Thus, even if 0( D) atoms are less abundant than 0( P), they play an important role in astrochemistry. They give highly reactive radical j)roducts as OH or NO which are for instance responsible for a significant reduction of the Eartlds ozone layer. The 0( D)+H2 reaction is also important in combustion chemistry. 

The phenomena observed in laboratory studies of plasmas also occur in extraterrestrial plasmas such as stars, interstellar and interplanetary media and the outer atmospheres of planets. The fact that cosmological implications of plasma interactions can be simulated in the laboratory opens up the possibility of studying astrophysicaJ phenomena in the plasma laboratory, as pioneered by Hannes Alfven. 

The field of applications of molecular quantum dynamics covers broad areas of science not only in chemistry but also in physics and biology. Historically, due to the fact that the full quantum-mechanical simulation of molecular processes is limited to small systems, molecular quantum dynamics has given rise mainly to important applications of astrophysical and atmospheric relevance. In the interstellar medium or the Earth atmosphere, molecules are generally in the gas phase. Since many accurate spectroscopic data are available, these media have provided various prototype systems to study quantum effects in molecules and to calibrate the theoretical methods used to simulate these effects. In this context, it is not surprising that much theoretical effort is still directed toward modeling the full quantum-mechanical treatment of small molecules. Among others, one can cite the studies of the spectroscopy of water [159-161], and of the spectroscopy, photodissociation. 

The SIFT is ideally suited to the study of the ion chemistries of the terrestrial atmosphere, TA, and interstellar clouds, ISC. These are ionized media in which gas phase ion-neutral reactions occur which produce the exotic ions and molecules observed in these regions. The challenge to ion chemists is to identify these reactions, and to this end the SIFT has made a major contribution. 

---