Separation of contributions to the third-order signal: ultrafast frequency-selected vibrational echo experiments on a metalloporphyrin-CO

One-dimensional and frequency-selected vibrational echo experiments on the CO stretching mode of a metalloporphyrin carbonyl compound (model heme) in poly-methylmethacrylate (PMMA) and in 2-methylteterahydrofuran (2-MTHF) are compared. Spectrally resolving the vibrational echo signal and observing the decay at selected wavelengths, permits the independent detection of the 0–1 and 1–2 vibrational level dephasing dynamics, eliminating cross terms and anharmonic beats. In the high temperature 2-MTHF liquid, 0–1 and 1–2 dephasing dynamics are identical within experimental error. The decays are non-exponential, demonstrating that the CO stretching mode absorption spectrum is not a completely homogeneous, motionally narrowed line.