Specular-Reflectance IR Spectroscopy of Polymethylmethacrylate Thin Films

The specular-reflectance technique has been used to develop an experiment for an undergraduate instrumental course that demonstrates the ability of Fourier transform IR spectroscopy to routinely procure vibrational spectra of thin films of polymethylmethacrylate on reflective copper discs. The experiment introduces students to the specular-reflectance technique and its selection rules, then demonstrates how they reveal the orientational constraint of adsorbed molecules within a thin film. Suggestions are included on how to expand the experiment to demonstrate the relationships between film thickness and the amount of light absorbed.