Ab initio studies of the low-lying π-states of borazine

Self-consistent-field and configuration-interaction studies were performed on borazine, using a double-zeta basis set augmented by six diffuse -functions. Low-lying singlet and triplet states of the A₁, A₂and E species were calculated, corresponding to ^* excited valence and Rydberg states. A selection out of singly and doubly excited configurations relative to a set of reference configurations was made for each species. Calculated vertical excitation energies (in eV) are 7.12 for ¹A₂(V), 8.45 for ¹E (3p-R), 8.57 for ¹A₁(V), 8.9 for ¹E(V-R), 9.55 for ¹E(3d-R), 6.98 for ³A₁(_V), 7.27 for ³E(V), 7.82 for ³A₂(V), 8.30 for ³E(3p-R), and 9.5 for ³E(3d-R), where V and R refer to valence or Rydberg character. The results are compared with experimental excitation energies, previous ab initio studies of borazine, and with recent ab initio studies of benzene.Dedicated to Professor Dr. H. Hartmann on the occasion of his 65th birthday.