The N = 1 → 0 transitions of CN and C 15 N (X 2 Σ +), as well as the J = 1 → 0 lines of HN 13 C and H 15 NC, have been observed toward 11 molecular clouds using the new 3 mm ALMA-type receiver of the 12 m telescope of the Arizona Radio Observatory. These sources span a wide range of distances from the Galactic center and are all regions of star formation. From these observations, 14 N/ 15 N ratios have been determined using two independent methods. First, the measurements of C 14 N and C 15 N were directly compared to establish this ratio, correcting for high opacities when needed, as indicated by the nitrogen hyperfine intensities. Second, the ratio was calculated from the quantity [HN 13 C]/[H 15 NC], determined from the HNC data, and then scaled by 12 C/ 13 C ratios previously established, i.e., the so-called double isotope method. Values from both methods are in reasonable agreement, and fall in the range ∼120-400, somewhat lower than previous 14 N/ 15 N ratios derived from HCN. The ratios exhibit a distinct positive gradient with distance from the Galactic center, following the relationship 14 N/ 15 N = 21.1 (5.2) kpc −1 D GC + 123.8 (37.1). This gradient is consistent with predictions of Galactic chemical evolution models in which 15 N has a secondary origin in novae, while primary and secondary sources exist for 14 N. The local interstellar medium value was found to be 4 N/ 15 N = 290 ± 40, in agreement with the ratio found in nearby diffuse clouds and close to the value of 272 found in Earth's atmosphere.

In this work Titan's atmospheric chemistry is simulated using a capacitively coupled plasma radio frequency discharge in a N(2)-CH(4) stationnary flux. Samples of Titan's tholins are produced in gaseous mixtures containing either 2 or 10% methane before the plasma discharge, covering the methane concentration range measured in Titan's atmosphere. We study their solubility and associated morphology, their infrared spectroscopy signature and the mass distribution of the soluble fraction by mass spectrometry. An important result is to highlight that the previous Titan's tholin solubility studies are inappropriate to fully characterize such a heterogeneous organic matter and we develop a new protocol to evaluate quantitatively tholins solubility. We find that tholins contain up to 35% in mass of molecules soluble in methanol, attached to a hardly insoluble fraction. Methanol is then chosen as a discriminating solvent to characterize the differences between soluble and insoluble species constituting the bulk tholins. No significant morphological change of shape or surface feature is derived from scanning electron microscopy after the extraction of the soluble fraction. This observation suggests a solid structure despite an important porosity of the grains. Infrared spectroscopy is recorded for both fractions. The IR spectra of the bulk, soluble, and insoluble tholins fractions are found to be very similar and reveal identical chemical signatures of nitrogen bearing functions and aliphatic groups. This result confirms that the chemical information collected when analyzing only the soluble fraction provides a valuable insight representative of the bulk material. The soluble fraction is ionized with an atmospheric pressure photoionization source and analyzed by a hybrid mass spectrometer. The congested mass spectra with one peak at every mass unit between 50 and 800 u confirm that the soluble fraction contains a complex mixture of organic molecules. The broad distribution, however, exhibits a regular pattern of mass clusters. Tandem collision induced dissociation analysis is performed in the negative ion mode to retrieve structural information. It reveals that (i) the molecules are ended by methyl, amine and cyanide groups, (ii) a 27 u neutral moiety (most probably HCN) is often released in the fragmentation of tholin anions, and (iii) an ubiquitous ionic fragment at m/z 66 is found in all tandem spectra. A tentative structure is proposed for this negative ion.