Ross D. Markwell

INFRARED SPECTROSCOPIC DETERMINATION OF THE GAS-PHASE THERMAL DECOMPOSITION PRODUCTS OF METAL-ETHYLDITHIOCARBONATE COMPLEXES

Abstract Head-space analysis by gas-phase infrared spectroscopy (HAGIS) allows the facile examination of the decomposition mechanisms of the metal xanthates [metal-( O -alkyldithiocarbonates], Fe(EtOCS 2 ) 3 , Zn(EtOCS 2 ) 2 , Cu(EtOCS 2 ), Pb(EtOCS 2 ) 2 and Ni(EtOCS 2 ) 2 , over the temperature range 25–120°C. These metal xanthates fall into two groups based on the generation of the primary gaseous decomposition products, CS 2 , COS and CO 2 . The first group, consisting of Fe(III) and Zn(II) xanthates, decompose readily, forming mostly CS 2 and COS in a constant ratio and leaving, initially, a metal-alkoxide residue. In the second group, decomposition is relatively small, generating CO 2 and COS, with the proportion of COS increasing as the temperature increases and CS 2 formation occurring only at the upper end of the temperature range. The residue is more of a metal-thioalkyl species in this case. Presumably, CO 2 is formed by re-insertion of COS into a metal alkoxide and elimination of CO 2 , leaving a thioalkyl moiety. Volatile metal-xanthates are probably observed in the gas-phase, allowing examination of the changes concomitant to the vaporization of the discrete metal xanthates from network or partially associated solids.

HEADSPACE ANALYSIS GAS-PHASE INFRARED SPECTROSCOPY : A STUDY OF XANTHATE DECOMPOSITION ON MINERAL SURFACES

Abstract The O -ethyldithiocarbonate (ethyl xanthate, CH 3 CH 2 OCS − 2 ) anion is a widely used reagent in mineral processing for the separation of sulphide minerals by froth flotation. Ethyl xanthate interacts with mineral powders to produce a hydrophobic layer on the mineral surface. A novel infrared technique, headspace analysis gas-phase infrared spectroscopy (HAGIS) has been used to study the in situ thermal decomposition products of ethyl xanthate on mineral surfaces. These products include CS 2 , COS, CO 2 , CH 4 , SO 2 , and higher molecular weight alkyl-containing species. Decomposition pathways have been proposed with some information determined from 2 H- and 13 C-isotope labelling experiments.

Spinning-Cell FT-Raman Spectroscopy: Application to Crystalline Octacarbonyldicobalt(0), Co2(CO)8

Raman spectrum of crystalline octacarbonyldicobalt(0), Co2(CO)8, has been successfully obtained for the first time by using a Fourier transform instrument together with a spinning sample cell to avoid decomposition of Co2(CO)8 upon exposure to the near-IR laser radiation used to excite the spectrum. Previously, only limited regions of the Raman spectrum could be obtained with visible laser excitation because of extensive sample burning. The new FT-Raman results, combined with the related IR data from the literature, provide a better description of the vibrational properties of this important binary metal carbonyl complex.

Pressure-tuning FT-Raman spectroscopic study of the T2g phonon mode of a diamond-anvil cell

Abstract The stress behaviour of a type-IIA diamond in a commercial diamond-anvil cell has been examined by measuring the position of the T2g phonon mode of the top diamond in the cell (originally located at ∼ 1332 cm−1) during a pressure-tuning FT-Raman microspectroscopic study at various pressures throughout the 0.001–62.2 kbar range. In general, the components of the scattered Raman signal from different depths appear as discrete band envelopes rather than a continuous gradient throughout the depth of the diamond. The changes taking place in the band structure with the variation in depth indicate the occurrence not of phase changes but of discontinuities in the pressure gradient throughout the diamond. For measurements made at the bottom edge of the diamond (i.e. at the sample-diamond interface), there is a linear relationship between the position (ν, wavenumbers) of the T2g phonon mode and the pressure (P, kbar) such that d ν d P = 0.16 cm −1 kbar −1 .

Pressure-tuning FT-Raman spectroscopy

Pressure-tuning dispersive Raman spectroscopy, using diamond anvil cells, has many of the common limitations of Raman spectroscopy such as low signal intensity, as well as photodecomposition and fluorescence of many samples. In the present investigations, the pressure-tuning experiment has been successfully coupled to an FT-Raman spectrometer using a microscope for sample alignment and measurement. The use of a holographic notch filter to eliminate the intense scattering due to the diamond anvil cell is discussed and studies involving organometallic complex, polymers, and biomolecules are presented.