Raman spectroscopic studies and DFT calculations on tribromoacetic acid and tribromoacetic acid-d

The Raman spectra of crystalline tribromoacetic acid (CBr3COOH), its deuterated analog (CBr3COOD) and a partially deuterated acid (CBr3COOD/H) have been measured using Raman spectroscopy. Density functional theory (DFT) calculations have been carried out in order to compare the measured spectra with the calculated ones and the bands have been assigned. The theoretical frequencies are close to the ones of the cyclic dimer in the crystal and this fact implies the “oriented gas” model for this compound. The three Raman active intermonomeric modes have been assigned. An extremely weak and broad (∼500 cm−1) νOH band for (CBr3COOH)2 centred at ∼3000 cm−1 could be detected. In addition, this band shows relatively sharp submaxima, irregularly spaced, assigned to overtones/summation bands of the COOH group. For the deuterated analog, (CBr3COOD)2 the OD stretching band is centred at ∼2230 cm−1 and shows sharp submaxima as well. In the solid state the tribromoacetic acid consists of dimers while in aqueous solutions the tribromoacetic acid is in monomeric form.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The Raman spectra of crystalline tribromoacetic acid (CBr3COOH), its deuterated analogue (CBr3COOD) and a partially deuterated acid (CBr3COOD/H) have been measured using Raman spectroscopy. ► DFT calculations have been carried out in order to compare the measured spectra with the calculated ones and band assignments have been carried out. ► The theoretical frequencies are close to the ones of the cyclic dimer in the crystal and this fact implies the “oriented gas” model for this compound. ► In the solid state the tribromoacetic acid consists of dimers while in aqueous solutions the tribromoacetic acid is in monomeric form.