Hydrogen bonding effect on Raman modes of Formic acid-water binary solutions

Abstract

Raman spectroscopy in combination with density functional theory (DFT) calculation was used to investigate the interaction between water and Formic acid. Raman spectra of formic acid (FA)-water binary solutions with different concentrations had been obtained at room temperature and ambient pressure. Gaussian deconvolution analysis was used for explaining the effect of FA on the OH stretching band. The frequencies of symmetric and asymmetric OH stretching mode changed significantly when the volume fraction of FA is 0.2 and 0.8 respectively, which attributed to the hydrogen bonding (HB) structure of water was affected, leading to FA-water structure undergo two phase transitions. Besides, the Raman frequencies of CO and CH stretching mode of FA also reverse at both two concentrations, which represent the main species of FA molecules were transformed. These results about the transition of FA-water structure and formic-formic acid structure were analyzed theoretically through Raman spectra and compared with the concrete details from density functional theory (B3LYP) calculations with 6-311++G(d, p) level.