Non-destructive NIR-FT-Raman analyses in practice. Part II. Analyses of 'jumping' crystals, photosensitive crystals and gems.
In: Fresenius' journal of analytical chemistry (Fresenius J.Anal.Chem.), Jg. 371 (2001) ; Nr. 7, S. 1018-1022
Zeitschriftenaufsatz / Fach: Chemie
Using an improved sampling arrangement the authors obsd. the FT Raman spectra of the different phases of a jumping crystal, an inositol deriv. The phase transition produced - as consequences of large changes of the unit cell consts. - changes in frequency and intensity mainly of CH deformation vibrations. Photochem. reactions, usually produced with light quanta in the visible range, are not activated with the quanta from the Nd:YAG laser at 1064 nm. The Raman spectra of the dark form of a dinitrobenzyl pyridine and afterwards the light form, the product of its illumination in the visible range, were recorded. The authors could not observe changes of most bands, esp. not of the NO2-vibrations; however, a new strong band appeared at 1253 cm-1, which may be due to the expected NH-photo-isomer. Genuine gemstones and fakes can be unambiguously identified by FT Raman spectroscopy. This is esp. useful for the stones whose phys. properties are quite similar to those of diamonds - moissanite and zirconia. The quality of diamonds can be estd. from relative band intensities; however, this is not in complete agreement with the internationally accepted visual qualification. Synthetic diamonds produced by CVD show remarkable differences from natural ones in their FT-Raman spectra.