LASER VAPORIZATION RARE-GAS MATRIX-ISOLATION ELECTRON-SPIN-RESONANCE STUDIES OF PDH2+, PDD2+, PDH, AND PDD - THEORETICAL INVESTIGATION OF PDH2+

The reactive laser vaporization of palladium metal in the presence of H2 (g) has been used to generate and trap neutral and charged palladium hydride radicals in neon and argon matrices for electron spin resonance investigations. The radicals identified are: 0PdH 2+, 105PdH2+, 0PdD2+, 105PdD2 +, 0PdH, 0PdD, 105PdH, and 105PdD. The electron spin resonance results prove that the H atoms are equivalent in PdH2+ but it cannot be determined for certain whether a highly bent 2A1 ground state complex or a linear 2Σ state is being observed, although the evidence seems to favor the 2A1 state. The observed nuclear hyperfine properties (A and g tensors) are best accounted for by assigning the unpaired electron predominantly to 4dz2/5s orbitale on the metal in PdH2+ with only about 3% of the spin density on each H atom. Electron spin resonance results for PdH constitute the first observations for a diatomic metal hydride radical trapped in a neon matrix. The magnetic parameters (MHz) for 105PdH2+ in a neon matrix at 4 K are: g⊥ = 2.568(2); g∥ ≅ 1.92; A⊥ (105Pd) = - 713(2); A∥ ( 105Pd) = - 688(15); A⊥ (H) = 45(1). Multireference SCF (MCSCF) and configuration interaction (CI) calculations were conducted for PdH2+ to calculate the energies and gross population distributions in the lowest-lying electronic states. The lowest of these, the 2A1 state, has a calculated stabilization energy of 9.3 kcal/mol relative to Pd+ (4d9) + H2. © 1990 American Institute of Physics.