A titanium sapphire laser spectrometer along with velocity modulation detection was used to record, between 12 000 and 13 400 cm−1, the absorption spectrum of the Ã 2A1–X̃ 2B1 electronic transition of H2O+ produced in an ac glow discharge with a gas mixture of He/H2O. The Σ(0,7,0)–(0,0,0) transition has been observed at 13 411 cm−1 and revised rotational assignments are presented. The Δ(0,7,0)–(0,0,0) and Π(0,6,0)–(0,0,0) transitions have been observed for the first time, at 13 331 and 12 494 cm−1, respectively. The vibrational assignment follows the vibrational numbering of Brommer et al. [J. Chem. Phys. 98, 5222 (1993)]. The rotational analysis was performed using the combination differences technique. Strong perturbations are observed, they are tentatively explained in term of rovibronic interactions. A set of effective molecular parameters has been obtained for each vibrational level of the à state. The values of the spin–orbit parameter are reported, they illustrate the vibronic coupling between the two electronic states.

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