A comparative study on the nature and strength of O-O, S-S, and Se-Se bond

A computational study on dichalcogenide molecules (R2X2; X = O, S, Se; R = H, CH3, NH2) has been carried out employing B3LYP and MP2 levels using 6-31+G*, 6-311+G*, 6-311++G**, and PVDZ basis sets. The relative energies have been evaluated at G2MP2 also. The rotational barriers and bond dissociation energies indicate that S-S bond is stronger than Se-Se and O-O bond. NBO analysis at MP2/6-31+G* suggest the presence of partial π character between X-X bond that decreases in the order S-S > Se-Se > O-O. Fuki functions for nucleophilic and electrophilic attack fail to distinguish the reactivity of S and Se. The proton affinities of the O2H2, S2H2, Se2H2 decrease in the order Se > S > O.