What Is Hidden Underneath NIR Lineshape of Water?
摘要
The vibrational spectrum of water attracts significant scientific interest, particularly in the mid-infrared (MIR) region, which is characterized by strong fundamental bands associated with OH stretching vibrations. However, the overtones and combination bands in near-infrared (NIR) spectrum, though less studied, offers valuable complementary insights into water structure and properties. Liquid water is characterized by highly convoluted vibrational bands, and considerable focus has been placed on gaining understanding of the structures that contribute to the observed spectra. Typically, the attempts to deconvolute the water band lineshape in NIR region were based on the assumption that full correspondence can be found in the better studied MIR bands. In this study, vibrational spectra were simulated using anharmonic quantum chemical methods applied to a range of water species up to a pentamer. The resulting lineshape accurately captured the characteristic NIR spectral profile of water. Notably, the spectral lines in the NIR and MIR regions exhibit differences due to anharmonic shifts between water species, leading to variations in the order and bandwidth of the contributing bands. Moreover, the NIR absorption curves of the contributing species demonstrated complex shapes. These findings demonstrate that the NIR spectrum delivers unique information on the structure and properties of water that is not redundant with fundamental bands of water located in the MIR region.