Comparison of different optical processes of the two-dimensional infrared spectroscopy in the effect of intermolecular vibrational coupling calculated in the time domain: The case of liquid N,N-Dimethylformamide

A time-domain method for calculating two-dimensional infrared (2D-IR) spectra is developed and is applied to the case of the amide I band of liquid N,N-dimethylformamide. This method includes the effects of both the diagonal frequency modulations (of individual molecules in the system) and the off-diagonal (intermolecular) vibrational coupling. The effect of the off-diagonal vibrational coupling on the 2D-IR band profiles is examined. The band profiles for three types of 2D-IR optical processes are compared and discussed in relation to this effect.