Computational and experimental studies of Pt-2(+/-) PCL with ammonia are reported. While ammonia is dehydrogenated with either cluster type, the reaction efficiencies phi are quite different with phi = 0.27 for Pt-2(+)/NH3 [K. Koszinowski, D. Schroder, H. Schwarz, J. Phys. Chem. A 107 (2003) 4999.] and phi = 0.0033 for Pt-2(-)/NH3. DFT-based relativistic calculations are consistent with this distinct behavior, with maximum energies along the reaction path of -13.3 kcal/mol for the cationic and +1.4 kcal/mol for the anionic clusters relative to the reactants. The recently proposed mechanism for the Pt-2(+)/NH3 system [D. Xu. X.-Y. Chen, S.-G. Wang, Int, J. Quant. Chem. 107 (2007) 1985.] needs to be modified to account for the experimental findings. (C) 2007 Elsevier B.V. All rights reserved.