The importance of dihydrogen complexes HnGe(H-2)(+) (n=0,1) to the chemistry of cationic germanium hydrides: Advanced theoretical and mass spectrometric analysis

Investigations of [Ge,H-n](-/0/+) (n=2,3) have been performed using a four- sector mass spectrometer. The results reveal that the complexes HnGe(H-2)() (n=0,1) play an important role in the unimolecular dissociation of the me tastable cations. Theoretical calculations support the experimental observa tions in most instances, and the established view that the global minimum o f [Ge,H-2](+) is an inserted structure may need reexamination; CCSD(T,full) l cc-pVTZ//CCSD(T)/6-311 + + G(d,p) and B3LYP/cc-pVTZ studies of three low- lying cation states ((2)A(1) HGeH+, B-2(2) Ge(H-2)(+) and B-2(1) Ge(H-2)(+) ) indicate a very small energy difference (ca. 4 kcalmol(-1)) between (2)A( 1) HGeH+ and B-2(2) Ge(H-2)(+); B3LYP favours the ion-molecule complex, whe reas coupledcluster calculations favour the inserted structure for the glob al minimum. Single-point multireference (MR) averaged coupled-pair function al and MR-configuration interaction calculations give conflicting results r egarding the global minimum. We also present theoretical evidence indicatin g that the orbitar-crossing point implicated in the spin-allowed metastable dissociation HGeH+*- Ge(H-2)(+)*-> Ge++H-2 lies above the H-loss asymptote . Thus, a quantum-mechanical tunneling mechanism is invoked to explain the preponderance of the H-2-loss signal for the metastable ion.