Exploring the change of hydrogen bond evolution in NMP-H₂O solution through 2D Raman-COS spectra analysis

The transitions of Hydrogen Bond (HB) structure with in the cluster structures of NMP-H2O solutions was conducted by combining Density Functional Theory (DFT) calculations and Two-dimensional Correlation Raman Spectroscopy (2D Raman-COS). When V-NMP < 20 %, NMP molecule is incorporated into the tetrahedral structure of water through an "insertion" mechanism, by displacing some H2O molecules and establishing HB. This interaction strengthens the tetrahedral arrangement in water, causing the free OH bond length to be compressed. When V-NMP > 20 %, large amounts of NMP molecules were self-assembled through dipole-dipole alignment, and the NMP2H(2)O, NMPH2O, and 2NMPH2O clusters gradually substitute the tetrahedral structure of water, leading to the disruption of the HB network in water. Furthermore, it was observed that the pulsed laser beam accelerated the transition point of the HB structure in the NMP-H2O solution. This research provides references for the application of NMP in the fields of aqueous batteries from the view of HB with electrolyte.