Low-lying electronic states of Ge₂⁺: a pseudopotential MRD-CI study

Abstract

The potential curves of 26 electronic states of Ge₂ ⁺, most of them correlating with the first dissociation channel Ge⁺ (²P_u) + Ge(³P_g), have been investigated by using pseudopotential and multireference configuration interaction (MRD-CI) techniques. The ground state of Ge₂ ⁺ is X⁴Σ^- _g (σ² _uσ_gπ² _u), with R _e = 4·67 a ₀, ω_e = 256 cm^-1 and D _e = 2·91 eV (- 3·15 eV estimated). The adiabatic ionization potential Ge₂(X³Σ^- _g) → Ge₂ ⁺ (X⁴Σ^- _g) is 7·16 eV. The first excited state of Ge₂ ⁺ corresponds to 1²Π_u (σ² _uσ² _gπ_u), with T _e = 0·45 eV; this state can be generated by π_u ionization from Ge₂ X³Σ^- _g (σ² _uσ² _gσ² _u). Ionization from σ_u might break the Ge-Ge bond since the generated ionic states lie close or above Ge⁺ + Ge. A comparison among isoelectronic species indicates that the electronic spectrum of Ge₂ ⁺ resembles that of Si₂ ⁺, yet both being different from the C₂ ⁺ spectrum. In fact, most low-lying states of Si₂ ⁺ and Ge₂ ⁺ have the antibonding π_g(π*)MO occupied, whereas the states of C₂ ⁺ show a tendency to occupy σ_g or π_u.