CH3CN interstellar

A comparison may be made between the calculated J - 6—5 transition of CH3CN on the one hand and the interstellar and laboratory spectra on the other shown in Figs. 15 and 16. The latter figure presents the emission lines observed by Solomon et at. in Sgr B2 and the laboratory spectrum of this transition ob-... 

Fig. 16. Comparison of the interstellar emission spectrum of CH3CN with the laboratory absorption spectrum of the / = 6-5 transition. The interstellar emission spectrum is seen in the direction of Sagittarius B2, and shows the various values of K (Solomon et al., 1971). The line shapes of the laboratory spectra resemble a first derivative...

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-... 

In one laboratory exercise, students use a radio telescope to measure the emission spectra of selected molecules in astronomical sources, such as dense clouds and old stars. Molecular hyperfme structure, classical spectral patterns of linear and symmetric top species, and maser action are investigated. Another laboratory exercise was developed where students measure the rotational spectra of HCO, HCCCN, and CH3CN in the laboratory, and determine their unique spectroscopic properties. They then use their measurements to identify these molecules in interstellar gas. 

SIFT studies have shown that CH ions readily undergo termolecular association reactions with many known interstellar molecular species, including CO, H2O, HCN, NH3, CH3OH and CH3CN. These ion-molecule associations must surely proceed via radiative association in dense ISC, and in this way complex molecules can be formed, as is indicated in Figure 7. Thus these SIFT studies have been crucial in indicating the importance of radiative association reactions in ISC. 

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