The two cluster anions, PtMgH3(-) and PtMgH5(-), were studied by photoelectron spectroscopy and theoretical calculations. Experimentally-determined electron affinity (EA) and vertical detachment energy (VDE) values were compared with those predicted by our computations; excellent agreement was found. The calculated structures of PtMgH3(-) and PtMgH3 both exhibit η2-bonded H2 moieties. Activation of these H2 moieties is implied by the elongation of their bond lengths relative to the bond length of free H2. The calculated structures of PtMgH5(-) and PtMgH5 both exhibit all-hydrogen, five-member, σ-aromatic rings. These attributes are responsible for this anion's special stability.

We report a joint photoelectron spectroscopic and theoretical study of the PtAl(-) and PtAl2(-) anions. The ground state structures and electronic configurations of these species were identified to be C∞v, (1)Σ(+) for PtAl(-), and C2v, (2)B1 for PtAl2(-). Structured anion photoelectron spectra of these clusters were recorded and interpreted using ab initio calculations. Good agreement between theory and experiment was found. All experimental features were successfully assigned to one-electron transitions from the ground state of the anions to the ground or excited states of the corresponding neutral species.

Anion photoelectron spectroscopic and theoretical studies were conducted for the PdH(-) and PdH3 (-) cluster anions. Experimentally observed electron affinities and vertical detachment energies agree well with theoretical predictions. The PdH3 (-) anionic complex is made up of a PdH(-) sub-anion ligated by a H2 molecule, in which the H-H bond is lengthened compared to free H2. Detailed molecular orbital analysis of PdH(-), H2, and PdH3 (-) reveals that back donation from a d-type orbital of PdH(-) to the σ* orbital of H2 causes the H-H elongation, and hence, its activation. The H2 binding energy to PdH(-) is calculated to be 89.2 kJ/mol, which is even higher than that between CO and Pd. The unusually high binding energy as well as the H-H bond activation may have practical applications, e.g., hydrogen storage and catalysis.