Pump Slice Amplitudes: A Simple and Robust Method for Connecting Two-Dimensional Infrared and Fourier Transform Infrared Spectra

Ultrafast two-dimensional infrared (2D IR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy are often performed in tandem, with FTIR typically used to interpret and provide hypotheses for 2D IR experiments. Comparisons between 2D IR and FTIR spectra can also be used to examine the structure and orientation in systems of coupled vibrational chromophores. The most common method for comparing 2D IR and FTIR lineshapes, the diagonal slice method, contains significant artifacts when applied to oscillators with low anharmonicities. Here, we introduce a new technique, the pump slice amplitude (PSA) method, for relating 2D IR lineshapes to FTIR lineshapes and compare PSAs against diagonal slices using theoretical and experimental spectra. We find that PSAs are significantly more similar to FTIR lineshapes than diagonal slices in systems with low anharmonicity.