THz spectra of parabens at low temperature

Terahertz transmission spectra of methylparaben, ethylparaben, propyl-p-hydroxybenzoate and butyl-p-hydroxybenzoate were measured by terahertz time-domain spectroscopy (THz-TDS) at 7.8 K. While it was difficult to observe the THz absorbance peaks of these esters at room temperature (294.3 K), they could be observed at 7.8 K. The THz absorbance peaks of these materials were at a higher frequency at 7.8 K than that at room temperature. Density functional theory (DFT) was used to simulate the vibrational spectrum of ethylparaben to study the origin of the THz absorbance peaks. This research provides reference data for the spectral properties of parabens and the identification of their molecular structures and vibration modes in the terahertz range.