MILLIMETER AND SUB-MILLIMETER-WAVE SPECTRUM OF SELENIUM DIOXIDE, SeO2

Subject and Purpose. The work is aimed at investigating the spectra of the ground-state and a few of the excited vibrational states for the main isotopologues of the selenium dioxide molecule, SeO2, in order to provide a reliable basis for its further search in the interstellar medium. Method and methodology. The method is based on real-life measurements and onward analysis of the microwave rotational spectrum of the SeO2 molecule. The measurements are carried out with an automated millimeter wave spectrometer of the Institute of Radio Astronomy of the NAS of Ukraine, (Kharkiv, Ukraine), and the submillimeter-wave spectrometer of the V. N. Karazin Kharkiv National University (Kharkiv, Ukraine). Results. The measurements were carried out within a range between 70GHz and 500 GHz, where frequencies of about 650 rotational transitions were measured. Most of these belong to the 76SeO2 , 77SeO2 , 78SeO2 , 80SeO2 , and 82SeO2 molecules in their respective vibrational ground states. The rest of the lines can be assigned to isotopic species of the 76SeO2 , 77SeO2 , 78SeO2 , 80SeO2 , and 82SeO2 molecules in their excited vibrational state ν2 = 1, while in the case of 80SeO2 in the excited state ν2 = 2 as well. In addition, tentative assignments have been suggested for 10 transitions in the ground -state isotopic species of 77SeO2. Conclusions. The transitions between states characterized by quantum numbers J up to 70 and quantum numbers Kɑ up to 19, embracing the ground-state and first-, and second-order excited vibrational states of the 74SeO2 , 76SeO2 , 77SeO2 , 78SeO2 , 80SeO2 , and 82SeO2 molecules have been identified. Based on these assigned transitions, significantly improved estimates have been obtained for sets of rotational and centrifugal distortion constants, including octic ones, as well as for A-reduced Watson’s Hamiltonian in the Ir coordinate representation. The parameter sets obtained provide for reliable predictions for possible future astronomical search of the most abundant isotopic species of the SeO2 molecule.