Potential energy surfaces for insertion of Zr into H2

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Abstract
Potential energy surfaces of twelve electronic states of ZrH2 are constructed using a complete active space self-consistent field method (CASSCF) followed by mult-reference singles + doubles configuration interaction (MRSDCI) calculations. The Zr(3 F) ground state of zirconium atom has to surmount a barrier of 11 kcal/mole for insertion into H2. The excited Zr(1 D) state inserts into H2 almost spontaneously. The excited Zr(5 F) atom forms a weak complex with H2 and subsequently has to surmount a large barrier for insertion into H2. Three possible nearly-degenerate bent electronic states are found for ZrH2 (1 A 1, 3 B 1 and 3 A 1). The 1 A 1 ground state of ZrH2 was found to be 26 kcal/mole more stable compared to Zr(3 F) + H2. Mulliken population analyses reveal considerable 4d5s5p hybridization of the metal atom in the Zr-H bonds. The dipole moments of bent low-lying electronic states reveal that the ZrH bonds are ionic with Zr+H- polarity. The effects of ten-component 4f-type functions are also studied on the various electronic states of ZrH2.