Raman Scattering Spectra and DFT Computational Analyzes of Intermolecular Interactions in Trifluoroacetic and Its Solutions

Abstract

In this work, the mechanisms of molecular clusters formation in liquid trifluoroacetic acid were studied using Raman scattering spectra in different solutions. The polarized components of Raman scattering spectra corresponding of the C=O, O–H stretching bands of pure trifluoroacetic acid consist of three broad bands at 1734, 1754, and 1800 cm−1 with different depolarization ratios. When the acid is strongly dissolved in acetonitrile, the 1800 cm−1 spectral band belonging to the C=O band remains. The intermolecular interactions in the formation of trifluoroacetic acid monomer, dimer, and trimer, as well as clusters with water [CF3COOH + (H2O)n, n = 1–7] and acetonitrile [CF3COOH + (CH3CN)n, n = 1–2] molecules, were analysed using the density functional theory (DFT) method.

Nonstoichiometric Protic Ionic Liquids: The Role of Excess Acid in Charge Transport Mechanisms

“…Furthermore, the formation of two low-intensity bands upon dilution with excess acid is observed for the spectral region between 1700 and 1820 cm –1 (see Figure b). In pure trifluoroacetic acid, these bands were assigned to the CO stretching vibration v CO , with the band at 1740 cm –1 arising from dimeric trifluoroacetic acid and the one at higher wavenumbers at 1780 cm –1 from the monomer. , None of these bands can be found for the stoichiometric TEA TFA, which is due to the very low intensity of the Raman bands and the very small amount of neutral acid according to the integrals in NMR. For the nonstoichiometric TEA TFA, a band at 1730 cm –1 occurs, which can be assigned to dimers.…”