INFRARED MULTIPLE-PHOTON PHOTODISSOCIATION OF GAS-PHASE GROUP II METAL-NITRATE ANIONS

Infrared spectra of gas-phase metal-nitrate anions M(NO3)3-, where M=Mg2+, Ca2+, Sr2+ and Ba2+, were recorded by infrared multiple photon dissociation (IRMPD) spectroscopy. Photodissociation of each of the precursors produces NO3- through the elimination of a neutral M(NO3)2 unit. An absorption pattern characteristic of metal nitrates is observed in the IRMPD spectra, including the symmetric and antisymmetric NO3 stretches. The latter is split into high and low frequency components as a result of perturbation of the nitrate symmetry by complexation to the metal ion, and the magnitude of the splitting decreases following the trend Mg2+ > Ca2+ > Sr2+ ? Ba2+. The experimental spectra are in good general agreement with those obtained from density functional theory calculations