Temporal changes of intermolecular vibrational peaks in THz spectra analyzed by two-dimensional correlation spectroscopy

The terahertz (THz) absorption spectra of organic compounds were measured by THz time-domain spectroscopy (TDS) during 100-300 K The temporal changes in the absorption spectra with different temperatures were analyzed using the two-dimensional correlation spectroscopy (2DCOS) technology. By comparing the cross peaks corresponding to the intermolecular vibrational modes, we concluded that the high-frequency band could be attributed to the vibration of the structure and the low-frequency band to the vibration between the structures. The exact frequencies of the overlapping vibrational bands and their assignments provide a new means to inspect the thermal behavior of the intermolecular vibrational modes.