Dissociation energies for H-2 loss from Na+.(H-2)(1,2) and K+.(H-2)(1,2) clusters have been determined via temperature-dependent equilibrium measurements. D-0 = -Delta H-0 degrees = 2.45 +/- 0.2 and 2.25 +/- 0.2 kcal/mol for Na+-H-2 and H-2.Na+-H-2, respectively, and 1.45 +/- 0.2 and 1.26 +/- 0.4 kcal/mol for K+-H-2 and H-2.K+-H-2, respectively. Also, ab initio calculations on Na+.H-2 were carried out at the HF and MP2 levels with an extended basis set and compared with previous calculations on this system as well as with experiment. By extrapolating these purely electrostatic results to the first-row transition series, one can conclude that covalent interactions dominate the bonding in V+-H-2 and Co+-H-2 systems.