Conformation-induced vibrational spectral dynamics of hydrogen peroxide and vicinal water molecules

Abstract

We studied the conformation-induced spectral response of water molecules due to site-specific structural alterations of solvated hydrogen peroxide (H₂O₂) employing DFT-based first principles molecular dynamics (FPMD) simulations. Wavelet transform was used to determine the time-dependent frequencies of the hydroxyls of water molecules and the O–H stretch modes of H₂O₂. Shifts in the vibrational frequency of the hydrogen-bonded hydroxyls inside the solvation shell of H₂O₂ support multiple distinctive hydrogen bonding environments. This paper classifies two distinct hydrogen bond types inside the O–O_W solvation shell of H₂O₂, and the dynamical calculations provide a quantitative estimation of the relative hydrogen bond strength. We ascertain the reason for not observing the escape of water molecules from the hydrogen peroxide hydration shell, unlike the solvation shell of ionic solutions and neutral solutes. Besides, we provide a comprehensive analysis of the spectral shifts in the normalized frequency distribution, the time-dependent decay of frequency–frequency correlation functions, and the hydrogen bond length scale fluctuations. We also quantify the relative contribution of the cisoid and transoid conformers affecting the vibrational spectral signature of the vicinal water molecules. While the transoid conformers promote the hydrogen bonding interactions through the oxygen site (O⋯H_W), the cisoid conformers facilitate hydrogen peroxide–water hydrogen bond formation through the hydrogen site (H⋯O_W). These non-identical hydrogen bond associations stabilize hydrogen peroxide in water.