Analysis of the high-resolution spectrum of molecules in doublet electronic states: fundamental $\nu_3$ band of chlorine dioxide ($^{16}$O$^{35}$Cl$^{16}$O) in the ground electronic state $X^{2}B_{1}$

Using a Bruker IFS 125 HR Fourier spectrometer, the vibrational–rotational structure of the ClO$_2$ molecule band $\nu_3$ has been recorded with a resolution of 0.0015 cm$^{-1}$. This band has been analyzed using an improved model of the effective Hamiltonian and a new computer program developed to analyze vibrational–rotational spectra of free radical molecules with an open shell, taking into account spin-rotational interactions. About 4200 transitions belonging to this band have been assigned with maximum values $N^{\operatorname{max}}$ = 68 and $K_{a}^{\operatorname{max}}$ = 21. Subsequently, we have used these to determine a set of 13 spectroscopic parameters of the investigated vibrational state. The standard deviation results in the value $d_{\operatorname{rms}}$ = 2.4 $\times$ 10$^{-4}$ cm$^{-1}$.