Observed and Calculated Infrared Spectra of Pd(H2)1,2,3 Complexes and Palladium Hydrides in Solid Argon and Neon

Thermally evaporated and laser-ablated Pd atoms interact with H 2 in excess argon to form the side-bonded Pd(H 2 ) complex, which is characterized by 2971, 1507, and 950 cm -1 fundamental frequencies. These infrared absorptions are assigned to Pd(H 2 ) on the basis of the HD and D 2 shifts and DFT frequency calculations. Higher H 2 concentrations favor the Pd(H 2 ) 2,3 complexes, which exhibit 3038, 778 cm -1 and 2909, 730, 319 cm -1 fundamentals, respectively. These complexes involve electrostatic bonding owing to a small amount of charge reorganization. Higher Pd concentrations enhance absorptions due to a Pd--Pd(H 2 ) complex and the stable (PdH) 2 molecule with no H−H bond. This work shows that one neutral Pd atom cannot insert into a H 2 molecule but that two Pd atoms dissociate molecular hydrogen with no activation energy. Laser ablation produces energetic Pd atoms which also form PdH, electrons which are captured to give PdH 2 -, and radiation which ionizes H and yields Ar n H + in the matrix cage. Diatomic PdH also forms complexes with dihydrogen.