Publication
Names
  • M. Fastelli
  • B. Schmitt
  • P. Beck
  • O. Poch
  • A. Zucchini
  • P. Comodi
Title
Low temperature phase transitions in the visible and near-infrared (VNIR) reflectance spectra of (NH4)2HPO4 and (NH4)HSO4 salts.
Abstract
The detection of ammonium bearing crystalline solids in salt-water systems on icy bodies and solar system bodiescould provide information about the ascent of these salts from a deep reservoir within the hydrosphere. Due to their chemical-physical properties, NH4+ compounds play a key role both in the internal dynamics of celestial bodies and in the potential habitability of ocean worlds. In this work we analysed the reflectance spectra of two synthetic NH4+ salts: ammonium hydrogen phosphate (NH4)2HPO4 and ammonium hydrogen sulphate (NH4)HSO4 in the 1-4.2 μm spectral range at low temperature, between 110 and 290 K. For (NH4)2HPO4 we also examined the effect of three different grain sizes (150–125 μm; 125-80 μm; 80-32 μm). The collected reflectance spectra show absorption features related to NH4+ group overtone and combination modes in the 1-2.5 μm range. In particular, the bands located at ~1.09 μm (3ν3), ~1.30 μm (2ν3 + ν4), ~1.58 μm (2ν3), ~2.02 μm (ν2 + v3) and ~2.2 μm (v3 + v4) could be useful to discriminate these salts. The low temperature spectra, compared to those at ambient temperature, reveal finer structures, displaying sharper and narrower absorption bands. The selected NH4+-bearing salts are subjected to reversible low temperature phase transitions, which are revealed in the spectra by a progressive growth and shift of the bands toward shorter wavelengths with a drastic change of their depth. The collected cryogenic spectra can be directly compared with remote sensing data from planetary missions of the upcoming decade such as NASA’s Europa Clipper, and ESA’s JUICE and the newly launched James Webb Space Telescope..
Keywords
spectroscopy, bidirectional reflection, bidirectional reflectance spectra, data analysis, near-IR, grain size, low temperature, phase change, band position, band width, band intensity, band integrated intensity, band vibration mode, mineral, Ammonium hydrogen sulphate, Ammonium hydrogen phosphate, planet surface
Content
sample, spectral data, band list data, planetary sciences
Year
2022
Journal
Icarus
Volume
425
Pages
116321
Pages number
13
Document type
article
Publication state
published