Coherence transfer (CT) describes dynamic pathways in which nontrivial system-bath coupling leads to the interconversion of quantum superpositions, representing a quantum mechanical analog of population relaxation.1 Time dependent spectroscopic techniques such as transient absorption and two-dimensional spectroscopies previously identified signatures of CT in processes ranging from charge transfer in photosynthetic proteins2 to vibrational relaxation in small molecules. However, spectral overlap between CT and population relaxation pathways complicates the interpretation of experimental data. Computational models of CT are not always practical to implement, particularly for CT occurring between superpositions of vibrational energy levels.3 As such, identifying experimental methods to suppress vibrational CT could provide a convenient means of recovering population dynamics from time-dependent spectra.

Supporting this effort, we use two-dimensional infrared spectroscopy (2DIR) to investigate the carbonyl stretching region of ethylene carbonate dissolved in tetrahydrofuran. Although only one fundamental vibrational transition exists in this region, Fermi resonance coupling leads to the observation of multiple bands in the experimental spectra.4 Our 2DIR experiments reveal extensive evidence of CT in the carbonyl region. We investigate the role of Fermi resonance coupling in vibrational CT, utilizing isotope substitution to modify the Fermi coupling strength. We then compare signatures of CT between ethylene carbonate isotopologues and find a significant reduction of CT upon weakening the Fermi resonance coupling. These findings demonstrate that the effects of vibrational CT in 2DIR spectra can be suppressed by isotope substitution, and applications to other systems will allow for time-dependent vibrational spectroscopies to report on the population dynamics of a wider range of chemical systems.