Examination of the Autoionization of Water via H-D Exchange during Crystallization

Autoionization of water is a fundamental process in chemistry, yet a comprehensive understanding remains elusive. At ambient temperature, the low concentration of hydrated protons from autoionization leads to rapid H/D exchange in mixtures of H₂O and D₂O. At cryogenic temperatures, autoionization and H/D exchange are largely suppressed. Recently, our group used this fact to investigate diffusive mixing of H₂O and D₂O in layered nanoscale films prior to crystallization.¹ However, we observe significant H/D exchange occurring with the onset of crystallization in the films – hypothesized to be the result of autoionization of water associated with ferroelectric ordering in ice nuclei.² Here, we examine this process using layered films of H₂O and D₂O in ultra-high vacuum. Reflection absorption infrared spectroscopy is used to characterize the concentrations of H₂O, D₂O, and HDO and the fraction of crystalline ice as a function of time and temperatures between ~136 and 155 K.



¹ G. A. Kimmel, et al., “Translational diffusion in supercooled water at and near the glass transition temperature—136 K.” J. Chem. Phys., 162 (2025) 244505.

²R. Shi and H. Tanaka, “Homogeneous nucleation of ferroelectric ice crystal driven by spontaneous dipolar ordering in supercooled TIP5P water”, J. Chem. Phys., 151 (2019) 024501.