A quantitative study of coherent vibrational dynamics probed by heterodyned transient grating spectroscopy

•Heterodyned transient grating spectroscopy (het TG) is shown to be a highly insightful method for analyzing vibrational wavepacket motion in a complex organic molecule.•All findings are explained and modelled in a response function formalism.•The differences to and advantages of het TG over pump-probe spectroscopy and absolute TG are discussed.