High-resolution observation and analysis of the I2+ A ²Π _32,u-X ²Π _32,g system

Rotationally resolved absorption spectra of I2+ were recorded in 12 065-13 062 cm ^-1 region by employing optical heterodyne velocity modulation absorption spectroscopy. In total, 4054 lines were assigned to 24 bands in the A ²Π _32,u-X ²Π _32,g system spanning the vibrational levels υ ^′′ = 1-4 and υn′ = 11-19. The assigned lines were globally fitted and an error of 0.003 cm ^-1 was obtained. Rotational constants, B _υ, were used to derive equilibrium parameters B _e ^′′ = 0.03977725(77) cm ^-1, a _e ^′′ = 1.1819(24)×10 ^-4 cm ^-1, r e′′ = 2.584386(25) Å of the X ²Π _32,g state, and B _e ^′ = 0.0305787(37) cm ^-1, a _e ^′ = 1.2353(23)×10 ^-4 cm ^-1, r e′ = 2.94758(18) Å of the A ²Π _32,u state. Vibrational energies were used to derive ω _e ^′′ = 239.0397(55) cm ^-1, ω _ex _e ^′′ = 0.64951(87) cm ^-1 of the X ²Π _32,g state and ω _e ^′ = 138.103(11) cm ^-1, ω _ex _e ^′ = 0.45027(34) cm ^-1 of the A ²Π _32,u state. The A ²Π _32,u (υ _n = 13) state was found to be rotationally perturbed by the a ₄Σ1/2,u- (υ _n = 17) state through second-order spin-orbit coupling.