Reference Raman spectra of synthesized CaCl sub(2).nH sub(2 )O solids (n=0, 2, 4, 6)

The CaCl sub(2).nH sub(2 )O solids with n=0, 1, 2, 4, 6 are of importance in fluid geochemistry in both the Earth and Mars. Their unambiguous identification is thus essential. Raman spectroscopy either in laboratory or in the robotic planet exploration with Raman spectrometer may provide such identification. Published Raman spectra of these minerals were from either unknown, or poorly known or simply wrong samples. The aim of this work is to provide Raman spectra over the 100-4000cm super(-1) spectral range for these solids synthesized in capillary and unambiguously identified by X-ray diffraction. Raman spectra were collected at room temperature and at -172 degree C. First interpretations of the Raman spectra of the OH stretching and bending modes of water and of the low-wavenumber bands (100-1000cm super(-1)) are given according to the knowledge of their structure. The main Raman bands are given for their identification and will be helpful for ExoMars surface exploration in the next ESA-Exomars mission in 2016-2018. Raman spectra of CaCl sub(2).nH sub(2)O (n=0, 2, 4, 6) solids unambiguously identified by X-ray diffraction (XRD) are given in the spectral range 100-4000cm super(-1) at room temperature and -172 degree C. Band assignment is discussed over the whole spectral range. These new data are reference spectra for geochemical and planetology exploration. An original method of synthesis of these solids in capillary is validated and allows their study by both XRD and Raman spectroscopy.