Effects of temperature on terahertz spectra of caffeine/oxalic acid 2:1 cocrystal and its solid-state density functional theory

Abstract The effect of temperature on terahertz (THz) spectra of caffeine/oxalic 2:1 cocrystal and its vibrational mode was analyzed. Caffeine anhydrate and oxalic acid dihydrate were dissolved in an organic solvent, after which the solution was evaporated to produce caffeine/oxalic acid 2:1 (CA/OX) cocrystal. The prepared CA/OX cocrystals were measured by a continuous wave gallium phosphide THz spectrometer at several low temperatures. The peak resolutions of the cocrystal spectra were found to depend on the temperature. To assign the vibrational modes, a density functional theory simulation was applied. The measured THz spectra of CA/OX cocrystal at low temperatures agreed with the calculated vibrational mode.