Multiconfigurational Character of Repulsive A2Σg+ State Leaves Strong Signature in the Photodissociation Spectrum of Zn2+

TL;DR

The photodissociation spectrum of Zn2+ shows unexpected features due to the multiconfigurational nature of its excited state.

Contribution

The study reveals how multiconfigurational character in a repulsive state leads to a distinct spectroscopic signature.

Findings

The A2Σg+ state of Zn2+ has a multiconfigurational character with two dominant configurations.

The transition dipole moment reaches zero near the equilibrium distance, causing a dip in the spectrum.

The dip in the photodissociation spectrum is a direct signature of the state's multiconfigurational nature.

Abstract

For the excitation to a repulsive state of a diatomic
molecule,
one expects a single broad peak in the photodissociation spectrum.
For Zn2+, however, two peaks for the spin- and
symmetry-allowed A2Σg+ ← X2Σu+ transition are
observed. A detailed quantum-chemical analysis reveals pronounced
multiconfigurational character of the A2Σg+ state. The σg(4s)2σg(4p) configuration with
bond order 1.5 dominates at short distances, while the repulsive σg(4s)σu*(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 A2Σg+ state.

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