Coherent two dimensional spectroscopy with triply vibrationally enhanced infrared four-wave mixing

A triply vibrationally enhanced four-wave mixing method measures the frequency domain coherent two dimensional vibrational spectrum of Ni(CO)2(PPh3)2 and Ni(CO)3PPh3 by triply vibrationally enhanced four-wave mixing using two excitation frequencies. This technique probes the coupling between vibrational modes. Two different phase-matching geometries were used. One geometry involves single vibrational quantum transitions while the second involves at least one multiquantum transition. Strong cross-peaks were observed for the phase-matching geometry requiring single quantum transitions but no measurable cross-peaks were observed for the multiquantum phase-matching geometry.