Accurate ab initio calculation of the BeH molecule. I. The X 2Σ+ and A 2Π states

Results of calculations using a configuration interaction LCAO‐MO method are presented for the ${\mathrm{X\hspace{0.17em}}}^2{\Sigma }^{+}$ and ${\mathrm{A\hspace{0.17em}}}^2\Pi$ states of BeH. Apart from the 1s shell of Be, the correlation energy of the remaining three electrons is calculated quantitatively using an extended basis set and complete configuration interaction including all single, double and triple replacements. The calculated spectroscopic constants are in excellent agreement with available experimental data. The present calculations also predict a value of $D_e(\mathrm{BeH}{\mathrm{,\hspace{0.17em}X\hspace{0.17em}}}^3{\Sigma }^{+}\text{)=2.115\hspace{0.17em}}\mathrm{eV}$ , and dismiss the possibility of a potential maximum in the ground state potential energy curve.