Joint survey of the experimental high-resolution spectra of H16O37Cl and H16O35Cl with a reanalysis of the 2ν2 band

The study starts with a detailed analysis of all the high-resolution rovibrational transitions measured for the minor hypochlorous acid isotopologue H¹⁶O³⁷Cl, employing the Marvel (Measured Active Rotational-Vibrational Energy Levels) procedure. The survey considers 16 sources, the wavenumber coverage of the transitions extends from the microwave to the visible region, corresponding to 13 vibrational parent states. Experimental transitions data from older (1994, 1996, and 2000) sources, not published explicitly in the original papers, are presented in here for the first time; the newly reported transitions represent about one third of all the transitions assigned for H¹⁶O³⁷Cl. Then a minor update to the transitions and levels of H¹⁶O³⁵Cl published in J. Mol. Spectrosc. 384 (2022) 111561 is provided. Proper labelling and internal consistency of the transitions and the empirical rovibrational energies of H¹⁶O³⁵Cl and H¹⁶O³⁷Cl is enforced utilizing effective Hamiltonian (EH) and first-principles variational nuclear-motion computation results. An iteratively updated line list, based on empirical and EH rovibrational energy levels and first-principles intensities, is used to assign a significant number of new transitions in the $2{\nu }_2$ band (2300–2800 cm⁻¹) for both isotopologues. At the end, for H¹⁶O³⁵Cl/H¹⁶O³⁷Cl, from the total of 20 349/10 266 experimentally measured transitions considered, 20 119/10 124 could be validated, allowing the derivation of 5760/3933 empirical rovibrational energy levels with well-defined uncertainties. Improved parameters for an effective Hamiltonian corresponding to the $2{\nu }_2$ state are given. A comparison with data in the canonical spectroscopic line-by-line database HITRAN is also provided.