Symmetry breaking in linear ZnCl2+: A theoretical study

The four lowest excited states (2Πg2Πg, 2Πu2Πu, 2Σu+, and 2Σg+) of ZnCl2+ are calculated using the EOMIP-CCSD method and the spectroscopic constants are reported. It is found that all the states have linear structures, while the 2Πg2Πg and 2Σu+ states are noncentrosymmetric with two equivalent global minima due to the pseudo Jahn–Teller effect. The computed barriers between the two minima are 88 and 169 cm−1, respectively, being much smaller and more reliable than the previous published multi-configurational results because of inaccurate treatment of the static correlation in the latter. For the ground 2Πg2Πg state, anharmonic vibrational levels are also simulated using the finite element method. It shows that the configuration of the vibronic ground state is also noncentrosymmetric.