Hydrogen-bonded structure in aqueous sulfuric acid solutions

Abstract

X-ray and time-of-flight (TOF) neutron diffraction and Raman spectroscopic measurements have been carried out at 25°C on concentrated aqueous sulfuric acid solutions, (H 2SO 4) x(H 2O) 1−x, x = 0, 0.25, 0.5, 0.75 and 0.86, in order to investigate the hydrogen-bonded intermolecular structure in the solutions. The intramolecular parameters for regular tetrahedral SO 4 unit were determined from the least squares fit to observed X-ray and neutron interference terms in the range of Q ≥ 8 Å −1. The nearest neighbor intermolecular hydrogen-bonded distances, r O…O = 2.7 Å and r O…D = 1.7 Å, respectively determined from X-ray and neutron intermolecular distribution functions, exhibited both ∼0.2 Å shorter values than those reported for pure liquid water. The isotropic Raman spectra of O-H stretching region for solutions of higher H 2SO 4 content (x ≥ 0.5) indicated an extremely broadened band centered at 3030 cm −1, which corresponds to ∼300 cm −1 lower frequency shift compared with that for pure liquid H 2O. These results sugges the existence of strong hydrogen-bonded intermolecular interaction in these solutions.