Potential energy surfaces for the Pt2+H2 reaction

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Abstract
Potential energy surfaces for the Pt2+H2reaction are obtained using a complete active space multiconfiguration self‐consistent field (CAS‐MCSCF) method followed by multireference singles+double CI (MRSDCI) calculations. Several approaches of H2 such as parallel, perpendicular, collinear, end‐on with respect to Pt2 are considered. In addition, out‐of‐plane twist motions of hydrogens relative to the Pt–Pt bond are considered. The parallel approach was found to be most reactive in the 1 A 1 electronic state, which forms a c i s Pt2H2 saddle point after surmounting a barrier of ∼20 kcal/mol. The saddle point thus formed spontaneously transforms to a t r a n s Pt2H2, 1 A g ground state through an out‐of‐plane twist motion. The dissociation of H2 in the parallel mode of collision was found to be brought about primarily through the interaction of the d(δ) orbitals of the two Pt atoms with the H2 1σ g and 1σ* u orbitals. The spin–orbit effects were studied using a relativistic CI (RCI) method and found to be significant for Pt2H2. Spin–orbit coupling was found to induce an avoided crossing. This destabilizes the Pt2H2(1 A g ) molecular state with respect to the dissociated Pt2+H2. The energy separation between the Pt2H2 1 A g t r a n s minimum and the c i s saddle point was calculated at the MRSDCI level as 3 kcal/mol. We find that the reactivity of Pt2 with H2 varies as a function of electronic state and orientation.