Did you know that when you shoot a laser at a mineral, a tiny amount of the light reflected from the surface changes its wavelength / energy? This non-intuitive idea is the basis for an incredibly useful tool in the geosciences, physics, and chemistry: Raman spectroscopy!
In this module we will explore the history, instrumentation, and theory of Raman spectroscopy. We will also investigate uses of Raman spectroscopy in the geosciences.
Just like infrared spectroscopy, Raman spectroscopy measures transitions between vibrational states of matter. Unlike infrared spectroscopy, Raman spectroscopy uses changes in visible light that is reflected from the sample. Raman and infrared spectroscopies are complementary techniques, and the theory learned in this module will be useful in understanding the theory of infrared spectroscopy (Chapter 8).
It is necessary to understand the nature of chemical bonds and their vibrations (Chapter 6) and the nature of electromagnetic energy and light (Chapter 3) to learn about Raman spectroscopy.
At the end of this module, students should be able to:
- Describe the career of C.V. Raman, how he discovered the theory of Raman spectroscopy, and how he conducted experiments to demonstrate Raman scattering
- Describe applications of Raman spectroscopy in the geosciences
- Read and plot Raman spectra
- Describe the key parts of a Raman spectrometer
- Describe the purpose of each part of a Raman spectrometer
- Describe the Raman shift and Stokes and anti-Stokes scattering using a vibrational energy level diagram
- Explain how Raman selection rules determine which vibrational energies of a material can be observed in Raman spectra
- Use the concept of signal-to-noise ratio to explain why certain techniques are used to improve the quality of Raman spectra
- Describe how fluorescence can interfere with obtaining Raman spectra, and use techniques to minimize florescence
- Follow instructions to use the Ocean Optics Raman spectrometer at JMU
- Change parameters in acquisition of Raman spectra to improve quality
Plot Raman data and use a Raman database to identify minerals
Prior Knowledge and Skills
Chapter 3: Electromagnetic Energy
Chapter 6: Chemical Bonds
License and Attributions
Text written by Elizabeth Johnson, James Madison University (JMU)