Ammonium Salts as a Source of Small Molecules Observed with High-Resolution Electron-Impact Ionization Mass Spectrometry

Hänni, Nora Phillys; Gasc, Sébastien; Etter, Adrian; Schuhmann, Markus; Isaac R.H.G., Schroeder I; Wampfler, Susanne; Schürch, Stefan; Rubin, Martin; Altwegg, Kathrin (2019). Ammonium Salts as a Source of Small Molecules Observed with High-Resolution Electron-Impact Ionization Mass Spectrometry. Journal of physical chemistry. A, 123(27), pp. 5805-5814. American Chemical Society 10.1021/acs.jpca.9b03534

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Recent high-resolution in situ mass spectrometry at comet 67P/Churyumov−Gerasimenko visited by European Space Agency’s 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 = Cl−) and ammonium formate (B = HCOO−) (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 +···B−). 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.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Departement of Chemistry and Biochemistry
08 Faculty of Science > Physics Institute
10 Strategic Research Centers > Center for Space and Habitability (CSH)

UniBE Contributor:

Hänni, Nora Phillys; Gasc, Sébastien; Etter, Adrian; Schuhmann, Markus; Isaac R.H.G., Schroeder I; Wampfler, Susanne; Schürch, Stefan; Rubin, Martin and Altwegg, Kathrin

Subjects:

500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 570 Life sciences; biology
500 Science > 540 Chemistry

ISSN:

1089-5639

Publisher:

American Chemical Society

Language:

English

Submitter:

Dora Ursula Zimmerer

Date Deposited:

31 Jul 2019 15:04

Last Modified:

22 Aug 2019 15:23

Publisher DOI:

10.1021/acs.jpca.9b03534

BORIS DOI:

10.7892/boris.132125

URI:

https://boris.unibe.ch/id/eprint/132125

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