Photodissociation mechanism of MgN2+ ion-molecule complex. An ab initio MO study

Potential energy curves (PECs) for the dissociation of the MgN2+ complex have been calculated by means of the ab initio MO method for the ground (X(2) Sigma) and low-lying excited ((II)-I-2 and 2(2) Sigma) states. The PECs for the ground and the first excited states were bound with respect to both dissociation limits, Mg+(S-2) + N-2 and Mg+(P-2) + N-2, respectively. A linear structure was obtained as the most stable form of the complex on the ground state PEG. The Cl calculations showed that the first excitation energy ((II)-I-2 <-- X(2) Sigma) was red-shifted relative to that for free Mg+(P-1 <-- S-2) transition owing to the formation of an excited state complex with a pi interaction between Mg+(3p) and N-2(pi(NN)) The PEC for the second excited state (2(2) Sigma) has a strongly repulsive shape because of a sigma* interaction between Mg+(3p) and N-2(n sigma). The photodissociation and N-N bond activation mechanisms of the MgN2+ complex are discussed on the basis of the PEC characteristics.