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Infrared Spectroscopy Laboratory

Bio Rad (Digilab) Excaliber FTS 3000 spectrometer with microscope attachment.

The Department of Mineral Sciences is equipped with a Bio Rad (Digilab) Excaliber FTS 3000 spectrometer with a microscope attachment. This instrument is able to measure and quantify the amount of infrared radiation (IR) that is absorbed by molecular species such as OH, H₂O and CO₂ in minerals, volcanic glasses, plastics and many chemicals. In our applications, minerals are powdered and combined with IR transparent material (usually potassium bromide) or individual mineral or glass grains, often microscopic, are wafered and highly polished on both sides. Recently we have added liquid nitrogen freezing capability to a special (Linkham) sample stage that can also heat samples.

 

Volcanic glass wafer as viewed through the optical microscope. The area through which the infrared beam passes can be adjusted using four aperture adjustment knobs. The lightest colored square in the image is the area to be analyzed. The square is 100 microns on a side.

 

Linkham stage used for controlled heating and freezing experiments.

 

Dr. Elizabeth Johnson using the liquid nitrogen freezing attachment of the Linkham stage. Freezing mineral specimens can improve resolution of IR absorption bands. The stage can also be used to heat samples in order to make observations on the changes within a mineral as water is driven off.

 

The improvement in the infrared spectrum of a manganese oxide mineral from freezing. The uppermost curve shows sharper and more detailed peaks.

 

A 50 micron thick wafer of an olivine crystal with many (gray) glass melt inclusions. The melt inclusions were trapped as magma (liquid) in the growing olivine crystal. These inclusions often preserve the water and CO2 content of the original magma. Through the use of FTIR, the water and CO2 content of the melt inclusions can be readily measured. The olivine crystal is from Kilauea and is approximately 1 millimeter in length.

 

The infrared spectrum of the Hope diamond. Bands in the 1600-3800 cm-1 region are truncated. The lattice modes of diamond are the transverse optic (TO) mode, the Raman-active mode, and bands in the second and third phonon regions. The broad absorbance with a maximum at about 3000 cm-1 that tails off toward higher energies, as well as three sharper bands (2460 cm-1, 2799 cm-1, and 2928 cm-1) are due to substitution of small amounts of boron for carbon in the pure diamond structure. The other absorption features in the spectrum (the off-scale 3726 cm-1, as well as 4097 cm-1, 5041 cm-1, 5404 cm-1) are combination modes of the transverse optic lattice mode at 1290 cm-1 and the 2460 cm-1 and 2799 cm-1 boron modes.