Potential energy surfaces for Tc+H2 and Ru+H2 reactions

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Abstract
Potential energy surfaces of 12 electronic states of TcH2 and RuH2 are obtained using a complete active space MCSCF (CASSCF) followed by multireference singles + doubles configuration interaction calculations (MRSDCI). The 6S ground state of Tc has to surmount a barrier of 40 kcal/mol to insert into H2 while the 5F ground state of Ru inserts into H2 with a much smaller barrier of 8.5 kcal/mol. The excited 6D, 4D, and doublet states of Tc atom insert into H2 spontaneously. The ground state of TcH2 is a linear 6Σ+g state arising from the 6S state of the Tc atom, while the ground state of RuH2 is of bent equilibrium geometry with 3A2 symmetry. A nearly degenerate bent state of 3B1 symmetry also exists for RuH2 . The bent minima of TcH2 are at least 0.9 eV above the linear 6Σ+g ground state of TcH2 . The ground state of RuH2 is 35 kcal/mol more stable than Ru(3F) + H2 while the 6Σ+g ground state of TcH2 is 27 kcal/mol more stable than Tc(6S)+H2 . All the bent states of TcH2 and RuH2 are ionic exhibiting strong M+H− polar bonds. The M–H bonds are made of dsp hybrid bonds as evidenced from Mulliken population analyses.