An Instrument for Isomer‐Specific Action Spectroscopy of Charged Clusters: Electronic Spectra of C14+ and Ca@C60+

Interpreting the spectra of mixtures of different isomers is a persistent challenge in gas‐phase ion spectroscopy, particularly when dealing with large molecules. The ability of our new instrument to obtain spectroscopic information on carbon‐rich molecular ions in an isomer‐selected fashion is demonstrated. This approach relies on coupling drift‐tube ion mobility and mass spectrometry with spectroscopic interrogation in a cryogenic 3D Paul trap. The instrument provides the possibility to employ two action spectroscopy techniques: two‐color resonance‐enhanced photodissociation and messenger‐tagging spectroscopy, which together provide a versatile experimental framework for obtaining spectroscopic fingerprints of isomer‐selected molecular ions. The method is illustrated on the example of and . Additionally, the first demonstration of the feasibility of messenger‐tagging spectroscopy using helium as messenger in a 3D Paul trap is reported.