Ammonia interstellar

The above examples should suffice to show how ion-molecule, dissociative recombination, and neutral-neutral reactions combine to form a variety of small species. Once neutral species are produced, they are destroyed by ion-molecule and neutral-neutral reactions. Stable species such as water and ammonia are depleted only via ion-molecule reactions. The dominant reactive ions in model calculations are the species HCO+, H3, H30+, He+, C+, and H+ many of then-reactions have been studied in the laboratory.41 Radicals such as OH can also be depleted via neutral-neutral reactions with atoms (see reactions 13, 15, 16) and, according to recent measurements, by selected reactions with stable species as well.18 Another loss mechanism in interstellar clouds is adsorption onto dust particles. Still another is photodestruction caused by ultraviolet photons produced when secondary electrons from cosmic ray-induced ionization excite H2, which subsequently fluoresces.42... 

Fig. 3.12 Model of an agglomerate consisting of many small interstellar dust particles. Each of the rod-shaped particles consists of a silicate nucleus surrounded by yellowish organic material. A further coating consists of ice formed from condensed gases, such as water, ammonia, methanol, carbon dioxide and carbon monoxide. Photograph Gisela Kruger, University of Bremen...

As already mentioned, hydrogen cyanide is formed in simulation experiments using reducing primeval atmospheres. CN was discovered in interstellar space as early as 1940 by optical spectroscopy (Breuer, 1974), and later HCN itself (from measurements using millimetre wavelengths). Only a few years after the Miller-Urey experiments, Kotake et al. (1956) obtained HCN in good yields by reacting methane with ammonia over aluminium-silicate contacts ... 

However, one of the electrical engineers at the University of California, Jack Welch, was willing to work with me, and I could use his radio antenna. So I had a student, Albert Cheung, take a look, and he looked at these dark clouds in space, and sure enough, there was ammonia. Well, since we found ammonia, we thought, we ought to look for water too, just to try this out. So the student looked, and there was water radiation. In fact it was very intense - hey, it had to be a maser, maser amplification in interstellar space And OH had already seemed to indicate something similar. 

The N-protonated form of HNSi, the H2NSi+ cation 69 and its possible isomers have been studied extensively by theoretical methods230-234. Bohme47 suggested that the ion 69, which is formed upon reaction of silicon cations with ammonia and subsequent dissociation of 69 upon electron capture (equation 33)235, is of prime importance for the formation of Si—N bonded species such as 67 in the chemistry of interstellar matter. 

Fig. 17. Energy levels of the rotation-inversion spectrum of ammonia. The quantum numbers (J,K) are given for each level. The heavy arrows indicate the inversion transitions detected in interstellar space and their frequencies in MHz. Thin arrows indicate the rotation-inversion transitions located in the submillimeter wave region. Dashed arrows indicate some collision induced transitions...

From the preceding discussions it is evident that at least four different temperatures have to be considered which under laboratory conditions are all equal the excitation temperature Tex of the molecule, defined by the relative populations of the levels, the kinetic temperature Tk, corresponding to the Maxwellian velocity distribution of the gas particles, the radiation temperature Traa, assuming a (in some cases diluted) black body radiation distribution, and the grain temperature 7, . With no thermodynamic equilibrium established, as is common in interstellar space, none of these temperatures are equal. These non-equilibium conditions are likely to be caused in part by the delicate balance between the various mechanisms of excitation and de-excitation of molecular energy levels by particle collisions and radiative transitions, and in part by the molecule formation process itself. Table 7 summarizes some of the known distribution anomalies. The non-equilibrium between para- and ortho-ammonia, the very low temperature of formaldehyde, and the interstellar OH and H20 masers are some of the more spectacular examples. 

In contrast to the CH3CN situation, the spectra of interstellar ammonia give considerable insight into excitation and de-excitation mechanisms. From the observed intensities of the interstellar ammonia lines it has been derived that the excitation temperature 7 12, determined from the relative intensities of the (1,1) and the (2,2) lines, is notably lower than the excitation temperature r13 determined from the intensities of the (1,1) and (3,3) lines. Thus the (3,3) level shows an excess population over the (1,1), (2,2) levels. In other words, ortho-ammonia is not in equilibrium with para-ammonia. However, a more detailed study of the two para-ammonia levels (1,1) and (2,2) also reveals that their relative populations are not given by a simple Boltzmann factor for each of them. The (1,1) level has population in excess over the Boltzmann distribu-... 

Ammonia was the first molecule for which the effect of the molecular inversion was studied experimentally and theoretically. Inversion in ammonia was subsequently found to be so important that this molecule played an important role in the history of molecular spectroscopy. Let us recall, for example that microwave spectroscopy started its era with the measurements " of the frequencies of transitions between the energy levels in the ground vibronic state of NH3 split by the inversion effect. Furthermore, the first proposal and realization of a molecular beam maser in 1955 was based on the inversion splittings of the energy levels in NH3. The Nobel Prize which Townes, Basov and Prochorov were awarded in 1964 clearly shows how important this discovery was. Another example of the role which the inversion of ammonia played in the extension of human knowledge is the discovery of NH3 in the interstellar space by Cheung and his co-workers in 1968, by measuring the... 

The vast stretches of space between the stars are by no means empty. They contain both gases and dust particles at very low concentrations. Interstellar space extends so far that these low-density species significantly affect the electromagnetic radiation arriving from distant stars and other sources, which is detected by telescopes. The gas in interstellar space consists primarily of hydrogen atoms (either neutral or ionized) at a concentration of about one atom per cubic centimeter. The dust (thought to be mostly solid water, methane, or ammonia) is even less concentrated, with typically only a few dust particles (each 10 " to 10 cm in radius) per cubic kilometer. 

Properties Colorless gas (or liquid) sharp, intensely irritating odor lighter than air easily liquefied by pressure. Bp -33.5C, fp -77C, vap press of liquid 8.5 atm (20C), sp vol 22.7 cu ft/lb (70C), d (liquid) 0.77 at 0C and 0.6819 at bp. Very soluble in water, alcohol, and ether. Autoign temp 1204F (650C). Combustible. Note Ammonia is the first complex molecule to be identified in interstellar space. It has been observed in galactic dust clouds in the Milky Way and is believed to constitute the rings of the planet Saturn. 

Dust particles of a size of several micrometers probably contained metals and condensates of water, ammonia, methane and admixtures of formaldehyde, acetonitrile, methylacetylene and other substances occurring in interstellar space. 

In the discussion above there are indications that ammonia is a common substance in space, distributed from grains (interstellar dust) over asteroids to satellites. Hence it is logical to assume that during the formation of the planet (icy) ammonia (and water and likely other substances) was carried to earth. The survival of ammonia would be extremely limited, first because the planetary bodies were soon molten after aggregation and will lose all volatiles (see Chapter 2.2.1) and form a primitive atmosphere. Secondly, most icy matter falling to the earth s surface would afterwards evaporate (by frictional heating) in that atmosphere, but it would input the volatile matter, e. g., ammonia and other substances (water, methane), which easily explains the first atmosphere (cf Table 2.7). 

Whether ammonia can react with simple carbonyls (formaldehyde, acetaldehyde, and acetone) at ultracold temperature in water clusters (i.e. interstellar ice analogues) has been examined theoretically. Almost barrier-free C-N bond formation was found for 4 X HjO clusters, with proton transfer becoming spontaneous at 9 x H2O. Consideration of what the teU-tale IR frequencies might be for such species in such clusters is also discussed. ... 

The reaction of N ions with molecular hydrogen to form NH ions was thought to initiate ammonia formation in interstellar clouds. Recently several experimental studies, either at very low temperature (Marquette et al, 1985b Luine and Dunn,... 

---