Reaction mechanism of platinum dimer cation with ammonia based on the relativistic density functional study

The gas‐phase reactions between Pt   2 +and NH 3 have been investigated using the relativistic density functional approach (ZORA‐PW91/TZ2P). The quartet and doublet potential energy surfaces of Pt   2 ++ NH 3 have been explored. The minimum energy reaction path proceeds through the following steps: Pt   2 + ( 4 Σ u ) + NH 3 → q‐1 → d‐2 → d‐3 → d‐4 → d‐Pt 2 NH + + H 2 . In the whole reaction pathway, the step of d‐2 → d‐3 is the rate‐determining step with a energy barrier of 36.1 kcal/mol, and exoergicity of the whole reaction is 12.0 kcal/mol. When Pt 2 NH + reacts with NH 3 again, there are two rival reaction paths in the doublet state. One is degradation of NH   4 +and another is loss of H 2 . In the case of degradation of NH   4 + , the activation energy is only 3.4 kcal/mol, and the overall reaction is exothermic by 8.9 kcal/mol. Thus, this reaction is favored both thermodynamically and kinetically. However, in the case of loss of H 2 , the rate‐determining step's energy barrier is 64.3 kcal/mol and the overall reaction is endothermic by 8.5 kcal/mol, so it is difficult to take place. Predicted relative energies and barriers along the suggested reaction paths are in reasonable agreement with experimental observations. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007