Accurate Frequency Determination of Vibration–Rotation and Rotational Transitions of SiH⁺

The fundamental ²⁸SiH⁺ ion has been characterized in a collaborative work, utilizing a hollow-cathode discharge laser spectrometer and a cryogenic ion trap spectrometer. Twenty-three vibration–rotation transitions around 4.75 μm have been detected with high accuracy. This has facilitated the first direct measurement of the pure rotational transition $J=1\leftarrow 0$ at 453056.3632(4) MHz in the trap spectrometer. The measured and accurately predicted transitions enable the search for this ion in space with IR and sub-mm telescopes.