A preprint study reports that Raman signals from ice became stronger near 0 °C in both liquid-nitrogen-frozen deionized water and ice made from calcium-chloride-saturated water. The calcium-chloride preparation also showed a larger drop in an intensity ratio, while the Raman-derived phase-window latent-heat metric was higher for the liquid-nitrogen sample. The authors present the pattern as an indirect signature and say it needs calorimetric validation.
Following the samples as they warmed
The comparison used two preparations: deionized water frozen in liquid nitrogen and ice made from calcium-chloride-saturated water. For each sample type, spectra were collected sequentially at minus 10 °C, minus 5 °C, 0 °C, 5 °C and 10 °C, with at least five minutes of equilibration at each step. The measurements used a Renishaw inVia Qontor Raman system with a 532 nm excitation laser.
To turn the spectra into comparable signals, the analysis integrated Raman intensity across the full O-H stretching range from 2600 to 3800 cm⁻¹. It also treated two narrower bands separately: 3080 to 3200 cm⁻¹ for the symmetric signal and 3300 to 3420 cm⁻¹ for the asymmetric signal. These integrated areas formed the basis for comparing how the two preparations changed as temperature rose.
The clearest differences appeared near 0 °C
Both preparations showed clear Raman-intensity enhancement near 0 °C. The integrated symmetric and asymmetric signals each developed a distinct peak near the transition, giving the experiment its clearest common feature.
The contrast emerged more clearly in a ratio-based measure of the spectral components. In liquid-nitrogen-frozen ice, the parameter changed sharply near 0 °C. In the calcium-chloride sample, it dropped at 0 °C, and the authors reported a larger intensity-ratio drop than in pure water.
A thermodynamic reading of the spectra
The paper places these observations in a thermodynamic framework linking heat absorbed during the transition with latent heat, enthalpy change and entropy change. In that setting, the Raman signal is being used as an indirect way to follow transition-related behavior, rather than as a standalone heat measurement.
An entropy-related response also separated the samples. The liquid-nitrogen-frozen preparation showed a sharp divergence in the entropy derivative near 0 °C, while the doped preparation showed fluctuations before and after the transition. The reported phase-window latent heat, based on a Raman-derived enthalpy-like metric, was higher for the pure liquid-nitrogen ice than for the calcium-chloride-doped ice.
The authors interpret the impurity-associated differences as consistent with a possibly lower latent-heat requirement for melting and altered entropy behavior. That reading remains a hypothesis about what the spectral changes represent, because the paper says differential scanning calorimetry could provide more precise latent-heat quantification and validate the proposed spectroscopic framework.
The test still to come
The paper compares a Raman-derived metric with latent heat, rather than reporting a direct calorimetric value. The study therefore supports a possible spectroscopic marker of the ice-water transition, but it does not by itself establish an absolute latent-heat measurement.
The central question of the preprint by Dongha Kim and Changyoun Lee is whether Raman changes can serve as an indirect marker of latent-heat-related behavior during the ice-water transition, and whether calcium chloride changes those signatures. The record identifies the manuscript as a preprint, so the result is presented as an early research report rather than a completed validation of the method.
Paper data and sources
Original title: Latent Heat and Raman Spectrum Change on Phase Transition of Water Including Calcium Chloride
Authors: Dongha Kim, Changyoun Lee
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-09-29
DOI: Not available
Original paper · Full text