Dibridged, monobridged, Y-shaped and linear structures of A2H2 molecules, with A = H, Li, Be, B, C, N, O and F. From acetylene to vinylidene

Abstract

CCSD(T)/aug-cc-pVQZ studies were performed on geometries and properties of dibridged, monobridged, Y-shaped (vinylidene-like) and linear HAAH and AHAH structures of A2H2 molecules, with A = H, Li, Be, B, C, N, O and F. Both singlet and triplet structures were studied for O2H2, only triplet structures for B2H2 and only singlet structures for the other molecules. Stable dibridged structures were obtained for Li2H2, Be2H2 and C2H2, stable monobridged structures for B2H2, C2H2, singlet and triplet O2H2. Be2H2, B2H2, C2H2 and N2H2 have stable Y-shaped structures with A-A as axis (A-AH2), whereas B2H2 and triplet O2H2 also have stable Y-shaped structures with H-H as axis (slightly distorted for O2H2). Stable structures with large interatomic distances were found, such as monobridged singlet and triplet O···HOH in Cs symmetry, Y-shaped Be···BeH2, B···BH2, H···HB2 in C2v symmetry and H···HO2 in Cs symmetry, as well as linear HBe···BeH and Be···HBeH. The energy difference between monobridged C2H2 and vinylidene ­is 1.395 kcal/mol with CCSD(T)/aug-cc-pVQZ and 1.363 kcal/mol with CCSD(T)/aug-cc-pV5Z.