Infrared spectroscopy of radioactive hydrogen chloride H³⁶Cl

We present the first report of optical absorption spectroscopy of H³⁶Cl, a radioactive isotopologue of hydrogen chloride. We used Fourier-transform infrared spectroscopy to determine the line center wavenumbers of the fundamental rovibrational band lines P(10)–R(10) and the first overtone band lines P(1)–R(7) with total uncertainty of less than 0.0018 cm⁻¹ (60 MHz) and 0.007 cm⁻¹ (0.2 GHz), respectively, at 68% confidence level. We also performed a rotational analysis on the bands to determine the related molecular constants. We further compared the linewidths and relative intensities of the lines to those of the stable isotopologues H³⁵Cl and H³⁷Cl. The new spectroscopic information assists in developing optical instrumentation for the detection of H³⁶Cl.