Compared to FTIR spectra, 2D IR spectra spread the information onto two frequency axes, which not only capture additional structural information through the 2D lineshapes and cross-peak intensities, but also access local environments around vibrational probes by the evolution of the lineshapes as a function of pump-probe delay ). In addition, while FTIR spectra require measuring a separate background of the buffer solution for subtraction, 2D IR spectra are often measured without a separate background. This is because, in water, the low oscillator strengths of the solvent vibrations and broad lineshapes naturally suppress the background, thus removing the necessity of background subtraction. Furthermore, given the narrow lineshapes in 2D IR spectra, small differences that can be difficult to observe in FTIR spectra are often easier to analyze in the corresponding 2D IR spectra, as such, it is often useful to extract a corresponding "1D" spectrum from a 2D IR spectrum . Recently, a robust method for extracting IR lineshape is the pump slice amplitude (PSA), which calculates the difference between the maxima and minima across a series of pump-axis slices through the 2D IR spectrum . The PSA method produces lineshapes comparable to FTIR spectra of the same system but with the advantages of eliminating artifacts due to anharmonicity and suppressing the background.