Low-Frequency Raman Spectra from Anhydrous Sulfuric and Chlorosulfonic Acids, and Liquid Water—Disruption of Tetrahedral Hydrogen Bonding—Relation to Water Structure

Abstract

Raman spectra from anhydrous sulfuric and chlorosulfonic acids, room temperature; and, water, 25 and (not shown) 300 °C; were obtained from a few to ≈400 cm− 1. Raman intensities indicate that tetrahedral hydrogen bonding in sulfuric acid may be a little more extensive than that in room temperature water. Tetrahedral hydrogen bonding does not occur in chlorosulfonic acid, and no significant Raman intensity was observed for it between ≈ 120 to 200 cm− 1, where hydrogen-bonded O-O stretching of O-H...0 units occurs. The low-frequency Raman spectra from room temperature chlorosulfonic versus sulfuric acid, bear the same qualitative relation to each other; as the corresponding spectra from water at 300 °C and 750 bar versus water at room temperature. Breakdown of tetrahedral hydrogen bonding in water with temperature rise may yield bifurcated hydrogen “bonds”, or similar interactions, which produce a 60–70 cm− 1 peak. Strong new evidence for a two-state model of water structure results from observation of two resolved intermolecular peaks having opposite temperature dependences.