Abstract
<title>Abstract</title> <p> Accurate values of the static dielectric constant of hydrogen are important for both fundamental thermophysical property calculations and emerging dielectric-based sensing applications in hydrogen liquefaction, storage, and processing systems. Previous work has shown that the existing reference correlations for hydrogen exhibit deficiencies at cryogenic conditions, particularly for <italic>ortho</italic> -rich hydrogen and liquid states. In this work, improved correlations are developed for the static dielectric constant of <italic>para</italic> - and <italic>ortho</italic> -hydrogen over temperatures from (1 to 1000) K. The low-density contribution was recalculated using modern <italic>ab initio</italic> rovibrational energy levels and state-dependent molecular polarizabilities. A new functional representation was developed that reproduces the temperature dependence of the first dielectric virial coefficient over the full temperature range considered, including the strongly non-linear behavior at cryogenic temperatures. An extensive review of the available dielectric constant measurements for normal and <italic>para</italic> -hydrogen was conducted, extending significantly upon the data used by previous dielectric correlations. These data were then used to develop revised correlations for the higher-density dielectric behavior of <italic>para</italic> - and <italic>ortho</italic> -hydrogen. The resulting correlations provide substantially improved agreement with available experimental data compared with previous models and better reproduce independent literature measurements that were not used in the fitting process, including recent measurements of the dielectric contrast between hydrogen spin isomers. However, the available experimental database remains limited, and the temperature dependences assumed for the higher-order terms remain only weakly constrained. </p>