Rotational Analysis of A²∏_u-X²∏_g System of ¹⁶O₂⁺ Cation

The Doppler-limited absorption spectrum of ¹⁶O₂⁺-1 by optical heterodyne velocity modulation absorption spectroscopy (OH-VMS). The transitions were assigned to the (2, 19), (3, 20), and (5, 21) bands in the second negative system (A²∏_u-X²∏_g). All the available lines measured using OH-VMS were global fitted in a nonlinear least-squares fitting procedure, and precise molecular con-stants (B_v, A_v, D_v, p_v, q_v, γ_v) were obtained for the involved levels.