Chiara Schleif

Rotationally resolved spectra of the HNC$^+$ and HCN$^+$ molecular ions have been recorded in the spectral range between 6200 and 6800 \rcm\ using a cryogenic ion trap instrument. The rovibrational transitions were probed using two different action spectroscopy schemes, namely laser-induced reaction (LIR) and leak-out spectroscopy (LOS). Various vibrational bands of HNC$^+$ and HCN$^+$ were measured with high resolution for the first time. For HNC$^+$, the $\text{X}~^2Σ^+~(20^00)-(00^00)$ overtone band was recorded using LIR, while LOS was used to probe the $\text{X}~^2Π~(000)^1-(210)^0μ$ combination band and the $\text{X}~^2Π~(000)^1-\text{A}~^2Σ^+~(10^00)$ vibronic band of HCN$^+$. Spectroscopic constants, band origins and radiative lifetimes for the observed states have been determined. The effective fit for the HCN$^+$ spectra revealed the presence of strong vibrational couplings leading to perturbations of the rovibrational levels of the excited states. The two action spectroscopy schemes are compared and their potential use to explore ion-molecule interactions is discussed.

This work presents the rovibrational spectra of the two strongest first overtone bands of the asymmetric stretching mode $ν_3$ ($2ν_3^{2+}$ and $2ν_3^{2-}$) 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 $2ν_3^{2+}$ and $6878.393(13)$ cm$^{-1}$ for $2ν_3^{2-}$.