Calculated ν2 (inversion) spectrum of H3O+

We report the observation and assignment of a number of vibration--rotation transitions within 1-reverse arrow1+ band of H3O+. The data are analyzed together with previously published measurements to yield a consistent set of rotational parameters that accurately reflects the vibration--rotation spectra involving the four lowest levels associated with the ν2 vibration of the ion. The analysis enables a precise estimate of the inversion splitting and the associated inversion-rotation spectrum of H3O+ which occurs in the far infrared