Gas Phase Preparation of the Elusive Monobridged Ge(μ-H)GeH Molecule through Nonadiabatic Reaction Dynamics

The hitherto elusive monobridged Ge(μ-H)GeH (X¹A′) molecule was prepared in the gas phase by bimolecular reaction of atomic germanium with germane (GeH₄). Electronic structure calculations revealed that this reaction commenced on the triplet surface with the formation of a van der Waals complex, followed by insertion of germanium into a germanium-hydrogen bond over a submerged barrier to form the triplet digermanylidene intermediate (HGeGeH₃); the latter underwent intersystem crossing from the triplet to the singlet surface. On the singlet surface, HGeGeH₃ predominantly isomerized through two successive hydrogen shifts prior to unimolecular decomposition to Ge(μ-H)GeH isomer, which is in equilibrium with the vinylidene-type (H₂GeGe) and dibridged (Ge(μ-H₂)Ge) isomers. This reaction leads to the formation of cyclic dinuclear germanium molecules, which do not exist on the isovalent C₂H₂ surface, thus deepening our understanding of the role of nonadiabatic reaction dynamics in preparing nonclassical, hydrogen-bridged isomers carrying main group XIV elements.