Isotope and mode selectivity in two-dimensional vibrational four wave mixing spectroscopy

Two-dimensional doubly vibrationally enhanced four wave mixing (2D-DOVE-FWM) spectra have been recorded for a mixture of CH3CN, CD3CN, and C6D6. Cross-peaks in these spectra indicate coupling between molecular vibrations that involve common vibrational modes. Modes are coupled by through-bond interactions and therefore the strongest cross-peaks are observed for vibrations on the same molecule. This coupling produces the vibrational anharmonicities that are required for multi-resonant four wave mixing. The absence of cross-peaks for different molecules demonstrates the isotope selectivity possible with doubly vibrationally enhanced (DOVE) spectroscopy. Model spectra were generated that account for the resonant spectral features observed.