A joint experimental and theoretical study of the infrared spectra of 2-methyl-4-nitroaniline crystals oriented on nanostructured poly(tetrafluoroethylene) substrates

The normal modes of vibration of crystalline 2-methyl-4-nitroaniline (MNA) deposited on nanostructured poly(tetrafluoroethylene) (PTFE) are investigat ed by means of polarized FT-IR Spectroscopy. As shown in a previous publica tion, the interface between the PTFE substrate and the MNA overlayer presen ts two distinct structures produced by an appropriate control of the experi mental growth conditions. In both cases, using a polarized beam oriented pa rallel or perpendicular to the PTFE sliding direction, we measured the dich roic ratios of the absorption peaks. The MNA molecule is also studied by me ans of ab initio quantum-mechanical methods to characterize the geometry an d the molecular normal modes of vibrations. On the basis of the structure o f the MNA/PTFE interface and the ab initio results, the experimental spectr a are thoroughly discussed, and the assignment of the most intense absorpti on peaks are proposed.