Hyperfine-resolved rovibrational and rotational spectroscopy of OH+ (X3Σ−)

Abstract

The OH⁺ (X³Σ⁻) 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 µm range and the spin manifold of the N = 1 ← 0 rotational transition around 1 THz have been extended and refined. Additionally, the spin manifold of the N = 2 ← 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.