2 research outputs found
Ammonium Salts as a Source of Small Molecules Observed with High-Resolution Electron-Impact Ionization Mass Spectrometry
Recent high-resolution in situ mass spectrometry at
comet 67P/ChuryumovâGerasimenko visited by European Space
Agencyâs Rosetta spacecraft raised the question, if sublimating
ammonium salts can unequivocally be detected in the cometary
coma. In laboratory experiments with the twin model of the space
instrument, two prototypic ammonium salts NH4B, namely, ammonium
chloride (B = Clâ) and ammonium formate (B = HCOOâ) (as well as
methodologically relevant isotopologues), were allowed to sublimate in
vacuum while mass spectra were collected. High-resolution electronimpact
ionization mass spectrometry provides an outstanding
experimental tool to investigate the complex physicochemical processes
occurring during the sublimation of ammonium salts. Sublimation of
ammonium chloride led to the observation of the ammonium cation
NH4
+ and the chloramide molecule NH2Cl in the neutral gas mode of the instrument. These observations could be jointly
interpreted as indirect evidence for the existence of a neutral gaseous parent species (either as the molecular complex NH3···HB
or the double-ionic species NH4
+···Bâ). However, the qualitative fragmentation pattern we present for 13C15N-ammonium
formate suggests an alternative route of NH4
+ production within the ionization region of the instrument, namely, by
protonation/hydrogenation. Besides NH4
+, other species were observed that were formed in protonation/hydrogenation
reactions. Moreover, together with the two major species from the decomposition of the salt, ammonia and formic acid, three
minor species also contributed to the fragmentation pattern: HCN/HNC, HOCN/HNCO, and CH3NO. Like chloramide,
formamide (CH3NO) also is a secondary species probably formed in a pseudo-intramolecular chemical reaction while ammonia
and the respective acid are in a state of association. HCN/HNC and HOCN/HNCO are ternary products coming out of
formamide decomposition reactions. We discuss our experimental findings, summarized in a tentative chemical reaction
network, in light of the available theoretical literature and highlight their relevance for the interpretation of in situ measurements
in space research.
1
Elemental and Molecular Abundances in Comet 67P/Churyumov-Gerasimenko
Comets are considered to be some of the most pristine and unprocessed solar system objects accessible to in-situ exploration. Investigating their molecular and elemental composition takes us on a journey back to the early period of our solar system and possibly even further. In this work, we deduce the bulk abundances of the major volatile species in comet 67P/Churyumov-Gerasimenko, the target of the European Space Agency's Rosetta mission. The basis are measurements obtained with the ROSINA instrument suite on board the Rosetta orbiter during a suitable period of high outgassing near perihelion. The results are combined with both gas and dust composition measurements published in the literature. This provides an integrated inventory of the major elements present in the nucleus of 67P/Churyumov-Gerasimenko. Similar to comet 1P/Halley, which was visited by ESA's Giotto spacecraft in 1986, comet 67P/Churyumov-Gerasimenko also shows near-solar abundances of oxygen and carbon, whereas hydrogen and nitrogen are depleted compared to solar. Still, the degree of devolatilization is lower than that of inner solar system objects, including meteorites and the Earth. This supports the idea that comets are among the most pristine objects in our solar system