Rotational analysis and isotopic effects in the A2Î u-X2Î g system for the O2+18 cation

The Doppler-limited absorption spectrum of the O2+18 cation was observed using a Ti-Sapphire laser system (in region of 12 060-12 800 cm−1) by optical heterodyne velocity modulation absorption spectroscopy. Precise molecular constants (Bυ, Dυ, pυ, qυ, γυ) were obtained for the involved levels by fitting spectral lines of (3, 20) and (4, 21) bands in the Second Negative system (A2Πu-X2Πg) using a nonlinear least-squares fitting procedure with the standard Hamiltonians. The vibrational assignment was based on the isotopic effect. More detailed isotopic effects on the molecular constants were discussed as well.

► We observed the absorption spectrum 12 060-12 800 cm−1 of O2+18. ► We assigned the spectral lines to the (A2Πu-X2Πg) system. ► The molecular constants were fitted for two vibrational bands and isotopic effects on molecular constants were discussed.