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

This study reports reliable theoretical evidence of the existence of a new diatomic molecule, the species BeB. Complementing previous invest igations predicting also the existence of new species like: BeN and Be C, it allows one to have now a global view of the properties and bondi ng of diatomics of beryllium with first/second row atoms. The electron ic structure was studied at the multireference single and double excit ations configuration interaction (MRSDCI) level as implemented in the MELD codes and with natural orbitals (for the (4) Sigma(-) state) as t he one-particle basis. Eighteen electronic states have been characteri zed with the ground state being a X(2)II with a relatively long equili brium internuclear distance (R(e) = 3.654 a(0)) and a small dissociati on energy (D-e = 0.86 eV). The next doubler is also weakly bound with R(e) = 3.982 a(0) and D-e = 0.48 eV. These states are followed by two close-lying quarters at 0.568 eV (a(4) Sigma(-)), R(e) = 3.246 a(0), a nd at 0.593 eV (b(4)II), R(e) = 3.460 a(0), with much deeper potential s, 3.04 and 3.02 eV, respectively. The curves crossings between these three excited states and another group of four doubler states lying: b etween 1.5 and 1.8 eV will certainly be responsible for a complex stru cture in the spectra of this molecule. Complementing the electronic de scription of all states, vibrational and rotational constants are also presented as well as dipole moment functions and vibrationally averag ed dipole moments. A graphical display of contour maps of the valence orbitals as a function of the internuclear distance clearly illustrate s the electron rearrangements occurring during molecule formation and the participation of beryllium 2p orbital in a pi-type bond. BeB shows more resemblance with the isoelectronic molecule B-2(+) rather than w ith BeC+. A comparison o,f the ground state spectroscopic properties o f BeB with the other first/second row beryllium diatomics is also pres ented.