The infra-red absorption spectrum of barytes
The infra-red absorption spectrum of barytes has been studied in the range 1 μ to 25 μ using ten different specimens, belonging to 001 and 110 sections. The extension of the range of study beyond 16μ has revealed the presence of fundamentals at 21 · 3 μ, (470 cm.−1) and 22 · 8 μ (439 cm.−1) besides other absorption maxima. The review of the available data shows that of the eighteen Raman active internal oscillations of barytes, fourteen can be identified including the one at 967 cm.−1 not previously recognised as such. The infra-red studies give ten of the fifteen theoretically possible infra-red active internal oscillations. The numerous absorption bands observed in the range studied find satisfactory explanation in terms of the infra-red active fundamentals in conjunction with the Raman active ones, applying selection rules appropriate to the unit cell of the crystal.