High-resolution observation and analysis of the I2+ A2Π(3/2,u)-X2Π(3/2,g) system.

Rotationally resolved absorption spectra of I(2)(+) 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(2)Π(3/2,u)-X(2)Π(3/2,g) system spanning the vibrational levels υ'' = 1-4 and υ(n)' = 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(2)Π(3/2,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(2)Π(3/2,u) state. Vibrational energies were used to derive ω(e)'' = 239.0397(55) cm(-1), ω(e)x(e)'' = 0.64951(87) cm(-1) of the X(2)Π(3/2,g) state and ω(e)' = 138.103(11) cm(-1), ω(e)x(e)' = 0.45027(34) cm(-1) of the A(2)Π(3/2,u) state. The A(2)Π(3/2,u) (υ(n) = 13) state was found to be rotationally perturbed by the a(4)Σ(1/2,u)(-) (υ(n) = 17) state through second-order spin-orbit coupling.