Coupling between C–D and CO motions using dual-frequency 2D IR photon echo spectroscopy

Coupling between C–D and CO vibrational modes of formamide has been characterized by dual-frequency 2D IR spectroscopy. The signals are consistent with those computed assuming an optically dense system at the CO frequency. A negative off-diagonal anharmonicity of ∼0.85 ± 0.20 cm−1 was obtained and the coupled modes have anticorrelated frequency distributions. Other features including relaxation times, diagonal anharmonicities for the individual CO and C–D modes and the dephasing dynamics of the cross peak have been determined to characterize the coupling between modes.