Dissecting the hydrogen bond network of water: Charge transfer and nuclear quantum effects

The molecular structure of water is dynamic, with intermolecular hydrogen (H) bond interactions being modified by both electronic charge transfer and nuclear quantum effects (NQEs). Electronic charge transfer and NQEs potentially change under acidic or basic conditions, but such details have not been measured. In this work, we developed correlated vibrational spectroscopy, a symmetry-based method that separates interacting from noninteracting molecules in self- and cross-correlation spectra, giving access to previously inaccessible information. We found that hydroxide (OH^-) donated ~8% more negative charge to the H bond network of water, and hydronium (H₃O⁺) accepted ~4% less negative charge from the H bond network of water. Deuterium oxide (D₂O) had ~9% more H bonds compared with water (H₂O), and acidic solutions displayed more dominant NQEs than basic ones.