Rearrangement of Langmuir-Blodgett stearic acid films and band assignments in deuterated stearic acid monolayers

Abstract

Band assignments in the C-D stretching region of straight chain hydrocarbon species are derived from the spectra of stearic acid monolayers on gold. The fatty acid molecules reorient with respect to the metal surface as the films age. Correlating the changes in the IR spectra of both the undeuterated and deuterated acids allows one to identify the vibrational modes of the latter based on the accepted assignments of the former. The CD₂ asymmetric and symmetric stretches are observed at 2194 and 2086 cm⁻¹, respectively. Bands at 2212 and 2221 cm⁻¹ are attributed to asymmetric in-plane and out-of-plane CD₃ stretches. Assignments of several other features in this region are given while one band remains unassigned.