Theoretical prediction on low-lying states of HBP and HPB radicals

Some low-lying states of the nine-valence-electron systems HBP and HPB radicals have been studied using three methods CASSCF, CASPT2, and B3LYP with the contracted atomic natural orbital (ANO) and cc-pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces were optimized at the CASSCF/ANO, CASPT2/ANO, and B3LYP/cc-pVTZ levels. The potential energy curves of isomerization reactions between HBP and HPB were calculated as a function of HBP bond angle. The calculated results indicated that the ground-state HBP is linear, while the ground-state HPB is bent, which is in contradiction to Walsh’s rules predicting linear structures for the HXY systems containing 10 or less valency electrons.