Vibration-rotation structure of the ν3 band of ClO2 was recorded with a Bruker IFS 125 HR Fourier spectrometer with a resolution of 0.0015 cm–1. Ro-vibrational analysis of the recorded experimental spectrum was made with an improved effective Hamiltonian and developed computer code for ro–vibrational spectra of open–shell free radical molecules including spin–rotation interactions. About 4200 transitions with the maximum values Nmax = 68 and Kamax = 21 belonging to the ν3 band were assigned and subsequently used to determine a set of 13 spectroscopic parameters of the vibrational state under study. The root-mean-square deviation of the results is drms = 2.4 ∙ 10-4 cm-1.

Using a Bruker IFS 125 HR Fourier spectrometer, the high-resolution spectrum of $^{16}$O$^{35}$\text{Cl}$^{16}$O molecule was recorded in the region of the $\nu_1+\nu_3$ band, in in which more than 2000 transitions with maximum values \textit{N}$^{max}$=59 and \textit{K}$^{max}_a$ = 16 were interpreted. The analysis of the obtained experimental information was performed on the basis of the model from ( Phys. Chem. Chem. Phys. 2021. V. 23. N. 8. P. 4580--4596) which takes into account the presence of spin-rotation interactions in the molecule. The standard deviation was $d_{rms}$ = 2.5 $\cdot 10^{-4} \text{cm}^{-1}$ and is 35 times higher than the result known in the literature.