On the reaction Mg+N2O→MgO+N2

The lowest singlet (1A′) and triplet (3A′) potential energy surfaces of the reaction Mg+N2O(1Σ+)=MgO+N2(1Σ+g) are investigated using ab initio SCF, two configuration MCSCF and CI wave functions. The reactivity of Mg(1S) and Mg(3P) is contrasted. These surfaces can be qualitatively partitioned into three contiguous, nondisjoint regions characterized by distinct values of an approximate reaction coordinate (ζ); a reactant region in which ζ≡ζ1≂R(Mg–O), a bending region in which ζ≡ζ2≂∢NNO, and a product region in which ζ≡ζ3≂(N–O). Evolution into region 3 requires Mg to N2O charge transfer which facilitates, and is facilitated by, bending of N2O. On the 3A′ surface which correlates with MgO(a 3Π), this process is largely downhill and involves an orbital reorganization in the N2O moiety for ζ=ζ3. A small barrier to vertical charge transfer is predicted at the CI level. On the 1A′ surface, which correlates with MgO (X 1Σ+) approach is uphill for ζ=ζ1. Possible explanations for the profound differences in the reactivity of calcium and magnesium with N2O are suggested.