Abstract <p>The oxidation of sulfur dioxide to trioxide on a vanadium catalyst was simulated using the Priroda&#xa0;6 quantum-chemical program. The active component of the catalyst is a complex compound containing vanadium pentoxide V₂O₅. This catalyst has found wide application in sulfuric acid technology at the stage of oxidation of sulfur dioxide. When studying sulfur oxides such as sulfur dioxide (SO₂) and sulfur trioxide (SO₃), it is important to evaluate their electronic states, low energy potential, and stability under the studied conditions. This can be useful for understanding the mechanisms of reactions involving these substances and predicting their behavior in different media. The probability of finding sulfur and its oxides in different multiplet states was taken into account in the calculations. The results of calculations prove the efficiency of using the vanadium catalyst, since the activation energy of the oxidation of sulfur dioxide to trioxide in the presence of a catalyst is one fifth the activation energy of the same process without a catalyst.</p>