Absorption Spectral Study On The A²Ⅱ_u-X²Ⅱ_g System Of The¹⁸O₂⁺Cation

Based on the known molecular constants and molecular structure of one isotopologue, we can analyze the spectra of the other isotologues and can further obtain their molecular constants and molecular structures employing the isotopic effect. The oxygen atom has three stable isotopes,16O,17O and18O, and the former is the richest one. Therefore, the spectral studies on the oxygen molecule are mostly about that formed by16O atoms. So are the studies about the molecular ion of oxygen, and few literatures are reported on18O2+cation.The thesis focuses on the spectral study of the rovibronic spectrum in the A2Πu X2Πg system of18O2+. Experimentally, the18O2+cations are produced by Penning discharging the flowing mixture of18O2and helium, and the spectra are recorded in the range of12060-12800cm-1employing optical heterodyne detected velocity modulation laser spectroscopy. Based on the known molecular constants of16O2+, the equilibrium constants of18O2+can be deduced via isotopic effect. So the band origins and Franck-Condon factors in this system of18O2+can be computed, and it can help us to assign the vibrational quantum numbers of the observed spectra. About203lines are assigned to the (3,20) band and174lines are assigned to the (4,21) band in the A2Πu-X2Πg system of18O2+. Adopting effective Hamiltonians of the two states, the molecular constants of the levels involved are obtained by the nonlinear least-squares fitting method.Additionally, the fitted molecule constants are in good agreement with those computed based on the isotopologue16O2+, which proves each other.