Density functional theory simulations of two‐dimensional infrared spectra for hydrogen‐bonded acetic acid dimers

Two‐dimensional coherent infrared spectra are simulated based on density functional theory calculations to analyze vibrational couplings in hydrogen‐bonded acetic acid dimers. Anharmonic sixth‐order force fields covering up to three‐body interactions are calculated for up to 11 normal modes. Three mechanisms for vibrational coupling within the two intermolecular hydrogen bonds are considered: anharmonic coupling of the high‐frequency OH stretching mode to low‐frequency modes, Fermi resonance coupling the of OH stretching mode to fingerprint mode combination tones, and a combination of both. Predicted coherent two‐dimensional infrared spectra show distinct signatures for the different coupling mechanisms.