As the most mature natural gas sweetening process, absorption has always been improved to meet the separation requirement. Recently, ultrasonic irradiation has been proposed as a technique that can intensify CO2 absorption. However, further studies are still required, particularly focusing on the sonochemical effect. Since the influence of the sonochemical effect on the reaction pathway is still debatable, attention must be given to verifying the influence of ultrasonic irradiation on the chemical reactions of CO2 absorption. Hence, this work aims to evaluate the influence of (Formula presented.)  radicals generated by the sonochemical effect on the chemical reactions involved during CO2 absorption using promoter-free methyldiethanolamine (MDEA). For the evaluation, various samples under irradiated and non-irradiated conditions are analyzed using the HPLC characterization technique. The results show that the hypothesis of changing the reaction pathway due to the presence of the sonochemical effect is invalid. However, it can accelerate the generation of hydroxyl radicals ((Formula presented.)) via water sonolysis. Thus, the origin of sonochemistry in aqueous solutions is defined as water sonolysis. The analysis of the CO2 absorption rate also demonstrates the presence of accelerated chemical reactions (contributed by the (Formula presented.)  radicals), which could potentially make the slow kinetic MDEA more practical for industrial application. © 2023 by the authors.