Ab Initio Potential Surfaces of BeH2+

Abstract

The potential surface of the BeH2+ molecular ion in C2υ geometries is computed by two ab initio methods: self-consistent-field (SCF) theory and valence bond configuration interaction (VBCI). Both calculations predict this ion to be weakly bound in a A12 state. A bound excited state of B22 symmetry is also predicted. According to SCF theory, the A12 state has a binding energy relative to H2 and (1s22s)2S Be+ of 0.19 eV, a BeH distance of 4.43 bohr, and a HBeH angle of 19.9°. The B22 state has a binding energy relative to H2 and (1s22p)2P Be+ of 3.2 eV, a BeH distance of 2.63 bohr, and a HBeH angle of 73.1°. SCF theory also gives an approximate ionization energy for BeH2 of about 9.71 eV. According to the VBCI calculation, the A12 state has a binding energy of 0.11 eV, a BeH distance of 4.16 bohr, and a HBeH angle of 20.5°, while the B22 state has a binding energy of 2.74 eV, a BeH distance of 2.76 bohr, and a HBeH angle of 93°. These ab initio results plus some experimental data for related ions strongly indicate that BeH2+ exists in two stable states which should be observable in mass spectrometers.