Theoretical study of B3O radical isomers and their interconversion pathways

Abstract

Despite the fact that B3O is the second simplest B n O radical after BO, a controversy recently emerged concerning the molecular structure of its global minimum. Two recent theoretical groups predicted the linear quartet BBBO to be the ground isomer. By contrast, another recent theoretical group reported that B3O has a doublet B3-ring ground structure. Moreover, larger B n O clusters usually have low-lying B3-ring isomers. In order to determine the accurate energetic competition between linear and cyclic structures in both the doublet and quartet, and to understand the detailed isomerism between various isomers, which is vital for understanding the formation mechanism of B3O, we report the first potential energy surface (PES) study of B3O at various computational levels, including CCSD(T)/6-311+G(2df), CCSD(T)/aug-cc-pVTZ, CCSD(T)/aug-cc-pVQZ and G3B3 for the single-point energy, as well as B3LYP/6-311+G(d) and QCISD/6-311+G(d) for geometrical optimisation. It is shown that the isomers in the quartet state are all thermodynamically more stable than the corresponding doublet ones, and on both the quartet and doublet PESs, the linear form has the lowest energy. Therefore, our study on both linear and cyclic isomers shows that the linear quartet BBBO 4 01 is definitively the ground isomer. Although being much less stable than the quartet linear BBBO global minimum by >20 kcal mol−1, five cyclic isomers exist as local minima, with the bi-cyclic structure 4 02 possessing the smallest barrier of around 15 kcal mol−1. The dissociation energies for direct combination processes B3 + O, B2 + BO and B + B2O are discussed. The present work may be helpful in obtaining a deep understanding of the doping and oxidation process of pure B n clusters.