Coherent Vibrational Dynamics and High‐resolution Nonlinear Spectroscopy: A Comparison with the Air/DMSO Liquid Interface

We present a comparative study on the C—H stretching vibrations at air/DMSO (dimethyl sulfoxide) interface with both the free‐induction decay (FID) coherent vibrational dynamics and the sub‐wavenumber high resolution sum‐frequency generation vibrational spectroscopy measurements. In principle the frequency‐domain and time‐domain spectroscopic measurements should generate identical information for a given molecular system. However, when the molecular systems are with several coupled or overlapping vibrational modes, obtaining detailed spectroscopic and coherent dynamics information is not as straightforward and rather difficult from either the time‐domain or the frequency domain measurements. For the case of air/DMSO interface that is with moderately complex vibrational spectra, we show that the frequency‐domain measurement with sub‐wavenumber high‐resolution sum‐ frequency generation vibrational spectroscopy is probably more advantageous than the time‐ domain measurement in obtaining quantitative understanding of the structure and coherent dynamics of the molecular interface.