A dataset of theoretical concentrations and ATR-FTIR spectra for quantitative analysis of water isotopologues (H<sub>2</sub>O, HDO, D<sub>2</sub>O)

<bold>Background</bold>The accurate molecular-level quantification of water isotopologues (H₂O, HDO, and D₂O) remains a significant analytical challenge in fields such as nuclear energy and materials science. Current standardized methods, including the Chinese National Standard GB/T 44647―2024, are limited to measuring total deuterium content using transmission-mode Fourier Transform Infrared Spectroscopy (FTIR) and cannot differentiate between HDO and D₂O molecules. This inability to distinguish individual species restricts advanced applications in heavy water reactor monitoring and deuterated material analysis. Although Attenuated Total Reflection-FTIR (ATR-FTIR) offers potential for in-situ and rapid analysis, a systematic methodology and public benchmark dataset for molecular-specific quantification are still lacking.<bold>Purpose</bold>This study aims to develop a robust quantitative method using ATR-FTIR spectroscopy to simultaneously discriminate and quantify H₂O, HDO, and D₂O molecules in heavy water samples.<bold>Methods</bold>A series of heavy water samples with varying initial D₂O concentrations were prepared as the research subjects. Spectra were collected using an ATR-FTIR spectrometer equipped with a diamond crystal under ambient temperature and constant pressure application to ensure optical contact and reproducibility. Then, three characteristic infrared absorption peaks, i.e., the H-O-H bending vibration (δ(H-O-H)) at about 1 640 cm^-1 integrated to quantify H₂O, the D-O-D bending vibration (δ(D-O-D)) at about 1 200 cm^-1 used for D₂O quantification, and the O-D stretching vibration (ν(O-D)) at about 2 500 cm^-1 applied to determining the total O-D bond concentration, were selected for quantitative analysis. Finally, the HDO concentration was indirectly calculated using the stoichiometric relation, and each sample was measured in triplicate to evaluate repeatability.<bold>Results</bold>Measured results show that this method demonstrates high precision, with all peak area measurements exhibiting a relative standard deviation (RSD) of less than 7% across five concentration levels, and excellent linearity observed in the calibration curves for all three species, with coefficients of determination (<italic>R</italic>²) exceeding 0.99. In blind testing, the deviation for D₂O quantification is +4.0%, and that for O-D bonds (directly related to HDO) is +3.3%. A larger deviation of -8.6% for quantification of H₂O may primarily be caused by interference from environmental moisture adsorption.<bold>Conclusions</bold>A novel, reliable, and practical ATR-FTIR-based method established in this study for the simultaneous quantification of H₂O, HDO, and D₂O, effectively overcomes the limitations of existing standards. The public release of the methodology and dataset provides a critical benchmark for future development of molecular-specific isotope analysis tools. These findings offer a valuable technical solution for real-time monitoring in nuclear reactors and precision detection in deuterated material research, with further improvements in H₂O accuracy expected through sample isolation techniques such as vacuum application.