This study reports reliable theoretical evidence of the existence of a new diatomic molecule, the species BeB.Complementing previous investigations predicting also the existence of new species like BeN and BeC, it allows one to have now a global view of the properties and bonding of diatomics of beryllium with first/ second row atoms. The electronic structure was studied at the multireference single and double excitations configuration interaction (MRSDCI) level as implemented in the MELD codes and with natural orbitals (for the 42-state) as the one-particle basis. Eighteen electronic states have been characterized with the ground state being a X211 with a relatively long equilibrium intemuclear distance (Re = 3.654 %) and a sinal1 dissociation energy (De = 0.86 eV). The next doublet is also weakly bound with Re = 3.982 and De = 0.48 eV. These states are followed by two close-lying quartets at 0.568 eV (a42-), Re = 3.246 ao, and at 0.593 eV (b4n), Re = 3.460 ao, with much deeper potentials, 3.04 and 3.02 eV, respectively. The curves crossings between these three excited states and another group of four doublet states lying between 1.5 and 1.8 eV will certainly be responsible for a complex structure in the spectra of this molecule. Complementing the electronic description of all states, vibrational and rotational constants are also presented as well as dipole moment functions and vibrationally averaged dipole moments. A graphical display of contour maps of the valence orbitals as a function of the intemuclear distance clearly illustrates the electron rearrangements occumng during molecule formation and the participation of beryllium 2p orbital in a n-type bond. BeB shows more resemblance with the isoelectronic molecule B2' rather than with BeC'. A comparison of the ground state spectroscopic properties of BeB with the other firsthecond row beryllium diatomics is also presented.

The theoretical vibrational spectra of P(4)O(6)X (X = O, S, and Se) molecules are determined by employing the Hartree-Fock method in combination with a basis set of double-zeta quality plus polarization functions. A comparison of the three spectra is undertaken, and the shifts of the vibrational frequencies found in the spectra are analyzed. Two effects are considered to explain the changes in the band positions: the mass effect due to the replacement of oxygen by sulfur and selenium, respectively, and the bond strength effect. The mass effect of the substituent is as important as the different bond strengths of the P(V)=X bonds. Previous assignments of the bands in the P(4)O(7) spectrum are also corrected by the theoretical research, and a new correlation among the experimental vibrational spectra of the three compounds is put forth. Newly performed Raman polarization measurements confirm our theoretical findings.

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In the present work the bonding situation within the P4O n (n = 6−10) series is studied using a combination of experimental and theoretical vibrational analysis. A correlation between the spectra of the compounds is undertaken, and the shifts of the vibrational frequencies within the series are analyzed. Our study shows that the frequencies of the most modes involving cage motions increase, when more oxygen atoms are added to the phosphorus centers. This reflects the reinforcement of the cage bonds along the P4O n (n = 6−10) series. For a few bands the frequencies decrease within the series, and this fact results from the reduced masses, which become larger with the increasing number of the substituents.

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