High-resolution Double Resonance Action Spectroscopy In Ion Traps: Vibrational And Rotational Fingerprints Of Ch₂nh₂⁺

Abstract

Applying various action spectroscopic techniques in a 4~K cryogenic ion trap instrument, protonated methanimine, CH$_2$NH$_2^+$, has been investigated by high-resolution rovibrational and pure rotational spectroscopy for the first time. In total, 39 rovibrational transitions within the fundamental band of the $\nu_2$ symmetric C-H stretch were measured around 3026\,cm$^{-1}$, which were used to predict pure rotational transition frequencies of CH$_2$NH$_2^+$ in the ground vibrational state. Based on these predictions, nine rotational transitions were observed between 109 and 283~GHz using a novel double resonance method. This method consists of rotational excitation followed by vibrational excitation, which is finally detected as a reduction in the number of CH$_2$NH$_2^+$-He complexes formed in the 4~K He bath of the trap.