Abstract: Based on density functional theory, the geometric optimization of thioglycolic acid molecules was performed at the B3LYP/6-311G(d,p) level, and the first 20 excited states of the molecules were calculated at the CAM-B3LYP/TZVP theoretical level. Firstly, the ground state information of the molecules was calculated and obtained. The results showed that when the center wavenumber of infrared spectrum number was less than 1856 cm^-1, the main vibrational mode of the molecules was bending vibration; when the center wavenumber of infrared spectrum number was greater than 1856 cm^-1, the main vibrational mode of the molecules was stretching vibration. Secondly, the first 20 excited states of the molecules were calculated, and four electronic state transitions with high transition probabilities (oscillator strength >0.05) were selected, and ultraviolet-visible spectra were plotted. Finally, the excitation types of these four transitions are determined by orbital pair transitions, and the excitation type of S0→S13 was charge transfer excitation; the excitation types of S0→S10 and S0→S11 were charge transfer excitation; the excitation type of S0→S20 was localized excitation. Studying thioglycolic acid, which is harmful to humans, can provide theoretical support for experimental research and provide a theoretical basis for subsequent research on its degradation.

Key words: thioglycolic acid, infrared spectrum, UV spectrum, hole-electron