The far-infrared spectrum of hypochlorous acid, HOCl

Spectra of hypochlorous acid, HOCl, have been measured in the 30–210 cm −1 interval with a practical resolution of 0.002 cm −1 . The spectroscopic analysis led to the assignment of 868 ground state rotational transitions (up to J = 54 and K a = 6) for HO 35 Cl, and 775 transitions (up to J = 49 and K a = 6) for HO 37 Cl. Moreover, 327 pure rotational transitions (up to J = 5) within the v 3 = 1 vibrational state of HO 35 Cl were also assigned. Improved sets of molecular constants were obtained for the ground states of both isotopic species from the simultaneous analysis of our far-infrared measurements and the microwave and millimeter-wave data presently available. On the other hand, the parameters derived for the v 3 = 1 state are very similar to those reported in the literature.