Polarised Infrared Spectroscopy: OH in Forsterite

Submitted by Tony Withers.

The image above is the starting frame from a QuickTime version of this updated mp4 movie embedded below:

[The] 6.5 MB QuickTime movie was the result of my first attempt at making polarised infrared measurements. The spectrum represents OH stretching vibrations in a crystal of olivine, synthesised under conditions of the earth's deep interior (80 kbar pressure, or 240km depth, and about 1000 C). The smooth curve is the sum of 5 Gaussian peaks. The indicatrix in the top right hand corner shows the height of those fitted peaks (radial distances) as a function of crystal orientation (we're looking down the c axis of the crystal). The coloured curves are fit to the polar data, and the interpolated peak heights derived from this fit are shown as vertical, colour-coded bars on the spectrum. The 'spectral data' are just linear interpolations of the real data, which gives a rough, but cool looking, indication of what happens as the polariser is rotated in the xy plane.

How this movie was created:

• Experiment was performed using the multianvil in the High Pressure Lab.
• Crystal was oriented using the microdiffractometer at the Institute of Technology Characterization Facility.
• Spectra were collected using SpectraTech cassegrainian microscope with ZnSd polariser and Nicolet FTIR 
• Peak fitting, data analysis and movie production using Igor Pro software.

Tony Withers' research page.