Reflectance Spectroscopy of Ammonium Salts: Implications for Planetary Surface Composition

Abstract

Recent discoveries have demonstrated that the surfaces of Mars, Ceres and other celestial bodies, as well as asteroids and comets, are characterized by the presence of ammonium-bearing minerals. A careful study of remote data compared with the analyses of more accurate laboratory data might allow a better remote characterization of planetary bodies. In this paper, the reflectance spectra of some ammoniated hydrous and anhydrous salts, namely sal-ammoniac NH4Cl, larderellite (NH4)B5O7(OH)2·H2O, mascagnite (NH4)SO4, struvite (NH4)MgPO4·6H2O and tschermigite (NH4)Al(SO4)2·12H2O, were collected at 293 and at 193 K. The aim is to detect how the NH4 vibrational features are affected by the chemical and structural environment. All samples were recovered after cooling cycles and were characterized by X-ray powder diffraction. Reflectance spectra of the studied minerals show absorption features around 1.3, 1.6, 2.06, 2.14, 3.23, 5.8 and 7.27 μm, related to the ammonium group. Between them, the 2ν3 at ~1.56 μm and the ν3 + ν4 at ~2.13 μm are the most affected modes by crystal structure type, with their position being strictly related to both anionic group and the strength of the hydrogen bonds. The reflectance spectra of water-rich samples [struvite (NH4)MgPO4·6(H2O) and tschermigite (NH4)Al(SO4)2·12(H2O)] show only H2O fundamental absorption features in the area from 2 to 2.8 μm and a band from hygroscopic water at 3 μm. Thermal analyses (TA), thermal gravimetry (TG) and differential scanning calorimetry (DSC) allowed to evaluate the dehydration temperatures and the occurring phase transitions and decompositions in the analyzed samples. In almost all samples, endothermic peaks at distinct temperatures were registered associated to loss of water molecules, differently linked to the structures. Moreover, an endothermic peak at 465 K in sal-ammoniac was associated to the phase transition from CsCl to NaCl structure type.

The Nature of Low-albedo Small Bodies from 3 μm Spectroscopy: One Group that Formed within the Ammonia Snow Line and One that Formed beyond It

“…Because none of these objects are seen to have NST spectra, this would also suggest that any ammonium salts present prearrival have disappeared since the meteorites fell. However, given the spectral properties of ammonium chloride (Fastelli et al 2020), it is not clear that the addition of ammonium salts alone to an otherwise ST spectrum would be able to reproduce the typical NST spectral shapes seen in the data set. A full explanation may involve a combination of differentiated and undifferentiated bodies and a range of relative amounts of ice and silicate accretion.…”

Ammonium chloride and urea based deep eutectic solvent: toxicological and antioxidant profile Authors

“…The FTIR spectra of DESs presented bands with characteristic functional groups of the precursors employed in the study. The FTIR spectrum of deep eutectic solvent based on ammonium chloride and urea, showed a single broad peak in the region of 3600-3000 cm -1 which was suggestive of hydrogen bonding between two molecules 16 . However, a few shifts were observed in the final FTIR spectrum of DES in comparison to its components such as the medium bend of urea amine (-NH) group had been shifted from 1687cm -1 to 1591cm -1 , a medium cyanide stretch of urea had also been shifted from 1148cm -1 to 1156cm -1 .…”

Evidence for Nitrogen-bearing Species on Umbriel: Sourced from a Subsurface Ocean, Undifferentiated Crust, or Impactors?

“…Although NH 4 chloride has a band center that is close to Umbriel's 2.2 μm band (∼2.21 μm), it is much broader than the features observed in spectra of Umbriel (Figures 4 and 5). Furthermore, these NH 4 salts exhibit strong absorption bands and/or prominent blue spectral slopes between 1 and 2 μm (Fastelli et al 2020), whereas Umbriel and the other classical Uranian moons exhibit neutral to slightly red surfaces over these wavelengths (Cartwright et al 2018) (Figures 6 and A1). Miranda is a possible exception as it is neutral to slightly blue over VIS and NIR wavelengths (Karkoschka 2001), but prominent, non-H 2 O ice absorption features are also absent from spectra of Miranda (Bauer et al 2002;Gourgeot et al 2014;Cartwright et al 2018;DeColibus et al 2022).…”