Identifying isotopes in HCl gas using high-resolution terahertz absorbance spectroscopy

This study presents a novel method for identifying the isotopes H35Cl and H37Cl using a unique high-resolution terahertz (THz) spectroscopy system. To prevent the absorbance of water vapor, chlorodimethylsilane (DMCS) was used as the source of HCl gas. Our analysis revealed periodic peaks at ∼1.9, 2.5, 3.1, 3.7, 4.4, 5.0, and 5.6 THz. Notably, we observed double peaks in the HCl isotopes H35Cl and H37Cl. The results were analyzed using least-square fitting, which showed that themeasurements agreed extremely well. The obtained peaks correlated with the rotational constants of HCl molecules, including 6B, 8B, 10B, 12B, 14B, 16B, and 18B.