Near-infrared high resolution overtone spectroscopy of the hydronium ion H ₃ O ⁺ : the 2ν ₃ ²⁺ and 2ν ₃ ²⁻ bands

This work presents the rovibrational spectra of the two strongest first overtone bands of the asymmetric stretching mode ν₃ (2ν₃²⁺ and 2ν₃^2-) of the hydronium ion, H₃O⁺. The measurements were performed in a temperature-variable cryogenic 22 pole ion trap using leak-out spectroscopy (LOS), covering an energy range of 6750-6950 cm^-1. The spectra were fit with a standard oblate symmetric top Hamiltonian and additional off-diagonal matrix elements accounting for <i>l</i>-doubling to obtain the spectroscopic constants and the band origins, which were determined to be 6845.610(14) cm^-1 for 2ν₃²⁺ and 6878.393(13) cm^-1 for 2ν₃^2-.