High resolution spectroscopy of asymmetric top molecules in nonsinglet electronic states: the nu(3) fundamental of chlorine dioxide ((OClO)-O-16-Cl-35-O-16) free radical in the (XB1)-B-2 electronic ground state

Highly resolved spectra of the (OClO)-O-16-Cl-35-O-16 isotopologue of chlorine dioxide were recorded with a Bruker IFS 125HR Fourier transform infrared spectrometer in the region of the nu(3) band. The analysis was made in the frame of the spin-rotational effective Hamiltonian (in A-reduction and I-r-representation) taking into account spin-rotational coupling operators up to the sixth order and the corresponding reduction of the Hamiltonian. The mathematical description of the ro-vibrational spectra was implemented to the specially created computer program ROVDES. Under the present experimental conditions, we were able to assign more than 5200 spin-rotational transitions to the nu(3) band. This number is 2.4 times higher compared to the previous studies available from the literature. The vibrational ground state parameters were improved, and the 2220 upper spin-rotation-vibration energy levels were determined and used as initial data in the inverse spectroscopic problem with the derived effective spin-rotational Hamiltonian. A total of 37 fitted parameters were determined (22 rotational and centrifugal parameters and 15 parameters of spin-rotation coupling). The appearance of strong Coriolis resonance interactions between the (001) and (100) vibrational states in the sets of (001)[N,K-a = 9], (001)[N,K-a = 17], (001)[N,K-a = 18] and (001)[N,K-a = 19] spin-rotation-vibration levels was experimentally observed for the first time and explained. The d(rms) = 1.4 x 10(-4) cm(-1) reproduction of the initial "experimental" upper ro-vibrational energy values was achieved which is considerably better compared to the use of parameters from a previous study ([J. Ortigoso et al., J. Mol. Spectrosc., 1992, 155, 25-43]).