Proton transfer chains in cold plasmas of H2with small amounts of N2. The prevalence of NH4+

Tandem MS Elucidation of the Late-Stage Degradation Mechanism of Nitroplasticizer

Understanding the degradation behavior of nitroplasticizer (NP) and the subsequent production of nitro-organics is crucial for both environmental monitoring and material development. A nontargeted approach via LC-QTOF-MS was employed to thoroughly study the degradation mechanism of NP in its late aging stage. Both positive and negative modes of ESI were performed to increase the compound coverage. To shed light on the fragmentation behavior of NP degradants (e.g., compounds containing a high density of NO2 moieties and oxygen sites) in the positive mode, which is rarely reported, the high-resolution tandem MS information on precursor ions at m/z 251(+), 254(+), 266(+), and 270(+) and a pair of isomeric ions at m/z 284(+) was investigated to extract their common diagnostic ions and dissociation channels, including the neutral loss of 2,2-dinitropropanol, nitro-nitrite rearrangement, homolytic cleavage of NO2, and simple inductive cleavage. Additionally, leveraging the sensitivity for nitroaromatics in the negative polarity, negative ions m/z 182(-) and 233(-) are identified as dinitroaniline and dinitronaphthol, respectively, which confirm the secondary hydrolysis pathway of the antioxidant (e.g., N-phenyl-2-naphthylamine) postulated in our previous work. In addition to earlier findings, the detection of these eight degradants further supports the evidence of increased acid concentration and aging temperatures in the late-stage NP environment, which contribute to intricate degradation behaviors in different aging environments.

Ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids

The measured nitrogen-to-carbon ratio in comets is lower than for the Sun, a discrepancy which could be alleviated if there is an unknown reservoir of nitrogen in comets. The nucleus of comet 67P/Churyumov-Gerasimenko exhibits an unidentified broad spectral reflectance feature around 3.2 micrometers, which is ubiquitous across its surface. On the basis of laboratory experiments, we attribute this absorption band to ammonium salts mixed with dust on the surface. The depth of the band indicates that semivolatile ammonium salts are a substantial reservoir of nitrogen in the comet, potentially dominating over refractory organic matter and more volatile species. Similar absorption features appear in the spectra of some asteroids, implying a compositional link between asteroids, comets, and the parent interstellar cloud.

Chemistry in glow discharges of H2 / O2 mixtures. Diagnostics and modelling

The chemistry of low pressure H2 + O2 discharges with different mixture ratios has been studied in a hollow cathode DC reactor. Neutral and positive ion distributions have been measured by mass spectrometry, and Langmuir probes have been used to provide charge densities and electron temperatures. A simple zero order kinetic model including neutral species and positive and negative ions, which takes into account gas-phase and heterogeneous chemistry, has been used to reproduce the global composition of the plasmas over the whole range of mixtures experimentally studied, and allows for the identification of the main physicochemical mechanisms that may explain the experimental results. To our knowledge, no combined experimental and modelling studies of the heavy species kinetics of low pressure H2 + O2 plasmas including ions has been reported before. As expected, apart from the precursors, H2O is detected in considerable amounts. The model also predicts appreciable concentrations of H and O atoms and the OH radical. The relevance of the metastable species O(1D) and O2(a1Δg) is analysed. Concerning the charged species, positive ion distributions are dominated by H3O+ for a wide range of intermediate mixtures, while H3+ and O2+ are the major ions for the higher and lower H2/O2 ratios, respectively. The mixed ions OH+, H2O+ and HO2+ are also observed in small amounts. Negative ions are shown to have a limited relevance in the global chemistry; their main contribution is the reduction of the electron density available for electron impact processes.