Using nylon-6 and polystyrene as prototypical materials with organic functional groups, we have demonstrated that for silicon or gold substrates, features due to the molecular vibrations can be seen in the ellipsometric spectra for films as thin as 50 Angstrom with signal-to-noise ratios ranging from 2 to 10. It is expected that with some additional optimization, this could be improved by a factor of 2 to 4. For films on a gold substrate, due to the high reflectivity, one would expect to be able to see these features for 10 A or thinner. For films on the glass substrate (or any other substrate that has an index of refraction near that of the film in the nonabsorbing region), IR ellipsometry provides thickness information that cannot readily be obtained from traditional ellipsometry. For all of the substrates, IR ellipsometry provides molecular structure information.