ELECTRONIC SPECTROSCOPY OF THE MG+-N-2 COMPLEX - EVIDENCE FOR PHOTOINDUCED ACTIVATION OF N-2

The ion-molecule complex, Mg+-N2 is formed in a supersonic expansion and studied with mass-selected photodissociation spectroscopy. The lowest energy bands observed in the electronic excitation spectrum are redshifted more than 12 000 cm-1 from the Mg+ (2P←2S) atomic transition at 280 nm. The red-shift, resulting from differential bonding in the ground and excited states of the complex, is much larger than the shifts observed in previously studied Mg +-ligand complexes. Resolved vibronic structure is observed extending for more than 5000 cm-1. The observation of spin-orbit multiplet structure indicates that the complex is linear and that the electronic transition is 2Π←X2Σ+. The spin-orbit splitting of 46 cm-1 is significantly less than that observed for other Mg+-L complexes. Vibronic intervals of about 1000 and 500 cm-1 are assigned respectively to a stretching mode and to double quanta in a bending mode. The study of isotopically substituted complexes indicates that the best assignment for the stretch progression is the N-N mode, with a frequency far below that in free N2. The vibrational activity, frequency shift, and spin-orbit splitting are all signatures for N2 activation by the excited metal ion. However, the degree of this interaction is greater than that predicted by ab initio calculations. © 1995 American Institute of Physics.