Hyperfine-Resolved Rovibrational and Rotational Spectroscopy of OH${}^{+}$ ($X^3{\Sigma }^{-}$)

Abstract

The OH${}^{+}$ ($X^3{\Sigma }^{-}$) radical cation has been investigated by combining a 4 K 22-pole ion trap apparatus with high-resolution IR and THz radiation sources. Applying different types of action spectroscopic methods, the fundamental vibrational band in the 3 $\mu$m range and the spin manifold of the $N=1\leftarrow 0$ rotational transition around 1 THz have been extended and refined. Additionally, the spin manifold of the $N=2\leftarrow 1$ rotational transition, scattered around 2 THz, has been measured for the first time with microwave accuracy. Although all hyperfine components of the pure rotational transitions are affected by considerable Zeeman splittings, a simulation of their contours allowed us to extract the field-free center frequencies with high accuracy. A global fit combining rovibrational and pure rotational transitions from the literature with those newly obtained in this work was performed, leading to improvements in the spectroscopic constants of OH${}^{+}$, particularly those in the ground vibrational state.

10 pages, including 2 figures, 5 tables, and references. In press at Phys. Chem. Chem. Phys