Near-infrared high resolution overtone spectroscopy of the hydronium ion H$_3$O$^+$: the $2ν_3^{2+}$ and $2ν_3^{2-}$ bands

Abstract: This work presents the rovibrational spectra of the two strongest first overtone bands of the asymmetric stretching mode $\nu_3$ ($2\nu_3^{2+}$ and $2\nu_3^{2-}$) of the hydronium ion, H$_3$O$^+$. 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 $l$-doubling to obtain the spectroscopic constants and the band origins, which were determined to be $6845.610(14)$ cm$^{-1}$ for $2\nu_3^{2+}$ and $6878.393(13)$ cm$^{-1}$ for $2\nu_3^{2-}$.