The alkaline earth dimer cations (Be2 +, Mg2 +, Ca2 +, Sr2 +, and Ba2 +). Coupled cluster and full configuration interaction studies†

Although all of the neutral alkaline earth dimers have been studied experimentally, only for the beryllium and strontium systems have the diatomic radical cations been subjected to modern spectroscopic techniques. In the present research, both coupled cluster and full configuration interaction methods were used to describe the M-2(+) systems. Basis sets as large as aug-cc-pCV5Z were chosen. For both Be-2(+) and Sr-2(+) agreement with the experiments is outstanding. Final predictions for the unknown dissociation energies are 10,651 (Mg-2(+)), 9605 (Ca-2(+)), and 8980cm(-1) (Ba-2(+)). The M-2(+) dissociation energies decrease monotonically going down the periodic except for the Sr-2(+) - Ba-2(+) pair. The unknown bond distances r(e) are 3.015 (Mg-2(+)), 3.814 (Ca-2(+)), 4.194 (Sr-2(+)), and 4.587 angstrom (Ba-2(+)).