The ground-state spectroscopic constants of Be-2 revisited

Abstract

Extensive ab initio calibration calculations combined with infinite-basis limit extrapolations lead to a ground-state dissociation energy of Be-2, D-e = 944 +/- 25 cm(-1), substantially higher than the accepted experimental value. Our best computed spectroscopic observables (experimental values in parentheses) are G(1) - G(0)= 223.7 (223.8), G(2)- G(1)= 173.8(169 +/- 3), G(3)- G(2) = 125.4(122 +/- 3), and Bo = 0.6086 (0.609) cm(-1) revised spectroscopic constants are proposed. Multireference calculations based on a full valence CAS(4/8) reference space suffer from unbalanced description of angular correlation; for higher accuracy, the (3s,3p) orbitals should be added to the reference space. The quality of coupled-cluster results depends crucially on the description of connected triple excitations. (C) 1999 Elsevier Science B.V. All rights reserved.