Theoretical Study of Sc²⁺, Ti²⁺, V²⁺, Cr²⁺, and Mn²⁺ Bound to H₂

The binding energies, vibration frequencies, and geometry of the high spin complexes of the dipositive transition metals, Sc 2+, Ti 2+, V 2+, Cr 2+, and Mn 2+, with molecular H 2 have been determined for all states correlating to the lowest term of the dipositive ion using multireference CI techniques. As expected, the bonding in these complexes is dominated by electrostatics (that is, enhanced by electron correlation) and varies smoothly across the sequence from Sc to Mn. The high spin complexes for Sc 2+, Ti 2+, V 2+, and Mn 2+ are the thermodynamic ground states for the MH 2 2+ system. For Cr 2+, however, the large second ionization energy of Cr results in the charge exchange reaction Cr 2+ + H 2 → Cr + + H 2 + being competitive with the electrostatic complex. The computed properties are compared with those for the corresponding monopositive ions.