MULTICONFIGURATION HARTREE-FOCK CALCULATIONS ON THE LOW-LYING STATES OF BERYLLIUM HYDRIDE

Abstract

Multiconfiguration Hartree-Fock calculations have been carried out on the states of beryllium hydride arising from the Be $(2^{1}S)$ and Be $(2^{3}P)$ manifolds. A near Hartree-Fock basis of Slater functions has been used. Configurations are included to allow proper dissociation and to take into account the 2s-2p degeneracy effect. The calculated and experimental spectroscopic constants for the ground state are given below (for the most accurate wavefunction computed to date): \begin{tabular} {lllllll} &\multicolumn {1}{c}{$R_{e}$} &\multicolumn {1}{c}{$D_{e}$} &\multicolumn {1}{c}{$\omega_{e}$} &\multicolumn {1}{c}{$X_{e}\omega_{e}$} &\multicolumn {1}{c}{$B_{e}$} &\multicolumn {1}{c} {$\alpha_{e}$} \\ Calc^{\prime}d &1.36 {\AA} &2.07 eV &$1979 cm^{-1}$ &$27.7 cm^{-1}$ &$10.0 cm^{-1}$ &$0.30 cm^{-1}$ \\ Expt^{\prime}1 &1.34 &$2.3 \pm 0.3$ &2059 &35.5 &10.3 &0.30 \\ \end{tabular} Although the ground state potential energy curve possesses a hump at R $\sim$ 2.9 {\AA}, its magnitude is so small, $\Delta E = 0.03 $eV, that it is of little importance. The $2^{2}\Sigma^{+}$ state is also bound, $D_{e} = 0.51 $eV, but with a much larger equilibrium internuclear distance than the ground state, $R_{e} = 2.51 {\AA}$. Calculations on the $1^{4}\Sigma^{+}$, $1^{2}\Pi$ and the $1^{4}\Pi$ states will also be discussed.