Nitrous oxide (N2O) is an intermediate compound in three-ways exhaust-pipes catalysis. Rh and Rh+ + N2O reactions are calculated at ab initio MRPT2 level, in C-s symmetry and for many multiplicities to find N2O capture and activation. Rh ground state does not capture N2O; however some excited states spontaneously capture and activate it, where only RhN2O (b (6)A') and (e (8)A '') activate N2O: RhN2O -> RhO + N-2 and RhN2O -> RhN2 + O, respectively but never break N-N bond. Rh+ ground state weakly capture N2O, but only one Rh+ excited state captures and activates N2O. N2O activation by Rh atom and cation do not involve any transition states. (C) 2010 Elsevier B. V. All rights reserved.