Quantitative Infrared Spectra of Hydrosilicates and Related Minerals

Abstract

Absorption coefficients associated with atomic motions of species expected in astronomical environments are determined from infrared measurements of various hydrosilicates, hydrated magnesium oxide, and the Al‐bearing chain silicate, sapphirine. Band types measured include O–H stretching modes near 3 μm, Si–O stretching motions near 10 μm, Si–O–Si bends near 14 μm, O–Si–O bends near 20 μm, and translations of cations such as Mg and Ca near 50–200 μm. We obtain data from films of varying thickness and use a ratioing method. First, bandstrengths of O–H fundamentals were determined from spectra obtained from films of controlled thicknesses, generally 6 μm. The O–H absorbance strength was then used to accurately determine thickness for a thinner film of each mineral (found to be <1 μm), thus providing bandstrengths of all other absorptions. Thin films were prepared such that the fundamental lattice modes showed intrinsic behaviour (i.e. band shapes were unchanged upon further thinning) and O–H modes are well resolved above the spectral noise. Bandstrengths were found to depend weakly on structure and should be applicable to other silicate minerals, allowing estimation of elemental concentrations independent of knowing the speciation of dust in astronomical environments. Comparison with observational data of NGC 6302 suggests that lizardite and saponite could be present in addition to refractory minerals.

The dehydroxylation of chrysotile: A combined in situ micro-Raman and micro-FTIR study

“…4, Table 1). Three bands at 301.7, 317.5, and 345.2 cm -1 whose assignments are still under discussion (Farmer 1974;Kloprogge et al 1999;Hofmeister and Bowey 2006) are an exception to this rule. They are located at lower wavenumbers with respect to the equivalent bands of lizardite-1T .…”

“…The latter uses the assignments of Kloprogge et al (1999) for other serpentine minerals also. However, band assignments of serpentine minerals are not straightforward and have to be taken with care considering the considerable discrepancies between the assignment schemes presented in previous investigations (Luys et al 1982;Kloprogge et al 1999;Rinaudo et al 2003;Hofmeister and Bowey 2006;Šontevska et al 2007;Prencipe et al 2009). A good example for such discrepancies are the diagnostic Raman bands between 620 and 635 cm -1 observed in experimental spectra of lizardite-1T and chrysotile.…”

“…In this context, the assignment of chrysotile bands at 301.7, 317.5, and 345.2 cm -1 is disputed. Kloprogge et al (1999) attribute these bands to bending modes of SiO 4 , whereas Hofmeister and Bowey (2006) assign them to Mg-O stretching modes. Their common negative shift compared to the frequencies observed in lizardite speaks for a common structural origin, i.e., all are either tetrahedral or octahedral modes.…”

Origin of HED Meteorites from the Spalling of Mercury - Implications for the Formation and Composition of the Inner Planets

“…Infrared dust emissions of the exploded circumstellar dust of NGC 6302 contain many peaks, consistent with the presence of pure, magnesium endmember silicates (forsterite, enstatite, and diopside), possibly calcium carbonate (Molster et al, 2001;Kemper et al, 2002), along with CAI minerals (Hofmeister et al, 2004). Hydrosilicates are possible (Hofmeister & Bowey, 2006). Dense dust clouds around young stellar objects contain ices (H 2 O, CO, CO 2 , CH 4 , hydrocarbons) thought to nucleate on the dust, summarized by Bowey and Hofmeister (2005) who identified melilite (a CAI phase) and Mg-rich amphiboles (hydrated pyroxenes).…”

Recent Results of Solid-State Spectroscopy

“…Hydrous silicates were also discussed to be a carrier of a broad 100 µm emission band detected in Herbig Ae/Be stars (Malfait et al 1999). Far-infrared absorption spectra of hydrous silicates have been measured by different laboratory astrophysics groups (Koike et al 1982, Koike and Shibai 1990, Hofmeister and Bowey 2006. The spectra show very interesting features such as the longest-wavelength phonon bands known to our knowledge (e.g.…”