Ga 2H 2: planar dibridged, vinylidene-like, monobridged, and trans equilibrium geometries

Abstract

The singlet potential energy surface of Ga 2H 2 has been studied using the self-consistent-field (SCF), single and double excitation configuration interaction (CISD), and single and double excitation coupled cluster (CCSD) methods. Optimized geometries and harmonic vibrational frequencies were obtained for four geometrical isomers with a double-zeta plus polarization basis set (DZP). Relative energies of the above structures were also predicted using a triple-zeta plus polarization basis set augmented with a set of f functions on the gallium atoms (TZP + f). For final energetic predictions with this basis set we included the effects of triple excitations perturbatively using the CCSD(T) method. The planar dibridged structure is the global minimum — two additional low-lying minima were found, corresponding to trans-bent and vinylidene-like structures. Our analysis also predicts the existence of a remarkable low-lying monobridged minimum, which has recently been observed experimentally for Si 2H 2, and predicted by ab initio methods for the valence-isoelectronic Al 2H 2.