A new hydrogen chloride (HCl) laser absorption diagnostic was developed and combined with a shock tube to obtain HCl time-history profiles behind reflected shock waves. An interband cascade laser was used to access the R(8) transition lines of the two isotopes H35Cl and H37Cl in the fundamental (1 \(\leftarrow\) 0) band at the specific wavelengths of 3045.06 and 3042.74 cm−1 near 3.3 μm, respectively. Spectroscopic parameters were obtained using HCl in 99.5% Ar, focusing on the line strengths and Ar-broadening effects, and were compared with theory from the literature. Experimental calibration of the HCl absorption coefficient and its dependence over a wide range of temperatures and pressures were obtained (i.e. 1261—1759 K, 0.25—0.42 atm, and 2390—3736 K, 1.26—2.00 atm). Measurements of the line strengths, Ar-broadening parameters at 296 K, and temperature-dependence exponents for the R(8) transition lines of H35Cl and H37Cl were validated against these results and can be summarized as follows: 1) For H35Cl: \({S}_{12}\left({T}_{0}\right)\) = 2.099 \(\pm\) 0.084 cm−2-atm−1, \({\gamma }_{H35Cl-Ar}\left({T}_{0}\right)\) = 0.0110 \(\pm\) 0.0005 cm−1-atm−1, and \({n}_{H35Cl-Ar}\) = 0.4 \(\pm\) 0.01.
2) For H37Cl: \({S}_{12}\left({T}_{0}\right)\) = 0.708 \(\pm\) 0.028 cm−2-atm−1, \({\gamma }_{H37Cl-Ar}\left({T}_{0}\right)\) = 0.0105 \(\pm\) 0.0005 cm−1-atm−1, and \({n}_{H37Cl-Ar}\) = 0.3 \(\pm\) 0.01.
The new HCl laser probe shows promising results for future measurements to better understand the combustion chemistry of propellants containing chlorine.
