LOW-LYING ELECTRONIC STATE OF GE-2+ - A PSEUDOPOTENTIAL MRD-CI STUDY

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 (MRDCI) techniques. The ground state of Ge2+ is X4-SIGMA(g)-(sigma(u)2-sigma(g)-pi(u)2), with R(e) = 4.67 a0, omega(e) = 256 cm-1 and D(e) = 2.91 eV (- 3.15 eV estimated). The adiabatic ionization potential Ge2(X3-SIGMA(g)-) --> Ge2+ (X4-SIGMA(g)-) is 7.16 eV. The first excited state of Ge2+ corresponds to 1(2)-PI(u)(sigma(u)2-sigma(g)2-pi(u)), with T(e) = 0.45 eV; this state can be generated by pi(u) ionization from Ge2 X3-SIGMA(g)- (sigma(u)2-sigma(g)2-pi(u)2). Ionization from sigma(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 pi(g)(pi*)MO occupied, whereas the states of C2+ show a tendency to occupy sigma(g) or pi(u).