Two-Dimensional Infrared Study of 13C-Natural Abundant Vibrational Transition Reveals Intramolecular Vibrational Redistribution Rather than Fluxional Exchange in Mn(CO)5Br

In this work, molecular-symmetry enhanced 13CO natural abundant isotopic infrared transition was identified in Mn(CO)5Br dissolved in CCl4 by FTIR spectroscopy. Diagonal and associated off-diagonal two-dimensional IR (2D IR) peaks of the 13CO-species were found to be spectrally separated from the all-12CO species, allowing a direct probe of the 13C natural abundant ensemble. Temperature-dependent FTIR experiment showed no evidence of ligand exchange in the metal carbonyl complex. Intramolecular vibrational redistribution dynamics among the CO stretching vibrational states were extracted using population-time dependent 2D IR diagonal and off-diagonal peaks for both radial mono-13CO and all-12CO isotopomers. This work demonstrates the potential use of natural abundant isotopic molecular species as a probe for revealing equilibrium and nonequilibrium structural dynamics in condensed-phase molecular systems.