Isolation and characterization of a peroxo manganese (III) dioxygen reaction intermediate using cryogenic ion vibrational predissociation spectroscopy

Abstract

We apply cryogenic ion vibrational predissociation (CIVP) spectroscopy to characterize the O2 attachment motif in a prototypical peroxo manganese (III) reaction intermediate. In this approach, species are extracted from solution using electrospray ionization and cooled in a 30K ion trap. The infrared spectrum is then obtained by monitoring the photoinduced evaporation of a single, weakly bound N2 molecule as a function of laser wavelength. Because the resulting CIVP action spectrum is linear in laser fluence, the pattern of well-resolved transitions can be directly compared with harmonic spectra calculated for predicted local minima using density functional theory (DFT). The assignment of the OO stretching band derived from the activated O2 ligand is established by following the evolution of the bands with 18O2 substitution, and the energy of this transition indicates that O2 is bound side-on to the Mn center. The successful application of CIVP to this class of compounds opens the way for sensitive spectroscopic characterization of weakly abundant species in complex solution environments.