A THEORETICAL-STUDY OF THE ELECTRONIC-STRUCTURE AND SPECTROSCOPIC PROPERTIES OF A NEW DIATOMIC MOLECULE, BEC

The 13 lowest-lying electronic states of a new diatomic molecule, BeC, are described theoretically for the first time using the multireferen ce single and double excitations configuration interaction approach. P otential energy curves are presented for all the states as well as a d escription of the electronic structure characterizing each of them. Di ssociation and vertical excitation energies, and dipole moment functio ns complete the electronic structure description. Vibrational and rota tional levels spacings, on the other hand, allowed the calculation of a whole set of spectroscopic constants characterizing each state. In i ts ground state, a 3SIGMA-, this molecule is more strongly bound (D(e) = 2.39 eV) than the recently described species BeN (D(e) = 1.34 eV) b ut still less strongly bound than BeO (D(e) = 4.69 eV) and BeF (D(e) = 5.82 eV). The first excited triplet state (3PI) shows an avoided cros sing at short internuclear distances which should certainly reflect in perturbative effects in its spectrum. A distinctive feature is also t he existence of a very low-lying strongly bound quintet state.