The molecular orientation of perfluorostearic acid [CF
3(CF
2)
16COOH] deposited by Langmuir–Blodgett technique has been investigated by grazing incidence reflection absorption and transmission infrared spectroscopy. In the former, the electric field vector is normal to the film surface whereas in the latter, it is parallel to the surface. The intensities of the infrared bands that tend to exhibit perpendicular polarization, e.g. symmetric stretching of
![](/images/glyphs/BO7.GIF)
COO
−, are much higher in reflection absorption than in transmission for deposited perfluorostearic acid. Therefore, these Fourier transform infrared results strongly support that the perfluorostearic acid molecules are preferentially oriented with their chain axes perpendicular to the substrate surface.