Study on the THz spectra of four kinds of Nipagin esters

The transmission spectra of methylparaben, ethylparaben, propylparaben, and butylparaben in the range of 0.2–2.5 THz are measured using terahertz time-domain spectroscopy (THz-TDS). Their refractive index and absorption spectra are obtained at room temperature in nitrogen atmosphere. The results show that the four kinds of Nipagin esters have obvious absorption peaks at 1.54 and 1.83 THz for methylparaben, 1.98 THz for ethylparaben, 1.37 and 1.61 THz for propylparaben, and 0.76 and 1.68 THz for