Multiconfigurational Character of Repulsive A 2 Σ g + State Leaves Strong Signature in the Photodissociation Spectrum of Zn 2 .

For the excitation to a repulsive state of a diatomic molecule, one expects a single broad peak in the photodissociation spectrum. For Zn 2 + , however, two peaks for the spin- and symmetry-allowed A 2 Σ g + ← X 2 Σ u + transition are observed. A detailed quantum-chemical analysis reveals pronounced multiconfigurational character of the A 2 Σ g + state. The σ g (4s) 2 σ g (4p) configuration with bond order 1.5 dominates at short distances, while the repulsive σ g (4s)σ u * (4s) 2 configuration with bond order -0.5 wins over with increasing bond length. The two excited-state configurations contribute with opposite signs to the transition dipole moment, which reaches zero near the equilibrium distance. This local minimum of the oscillator strength is responsible for the pronounced dip in the photodissociation spectrum, which is thus the spectroscopic signature of the multiconfigurational character of the A 2 Σ g + state.