Ion Trap Spectroscopy of Molecular Ions
Summary
Ion trap spectroscopy of molecular ions encompasses a suite of experimental techniques that confine charged molecules within radio-frequency or cryogenic multipole traps, cool them via buffer gas or sympathetic cooling, and interrogate their internal states with laser radiation. By stabilising ions at millikelvin to kelvin temperatures, researchers can record high‐resolution rovibrational and rotational spectra free from thermal broadening and collisional perturbations. The approach leverages action spectroscopy—where photonic absorption induces measurable changes such as fragment formation or motional excitation—to yield precise vibrational band centres, rotational constants and information on isotopic variants. Innovations such as helium‐tagging and novel detection schemes (for example, leak‐out‐spectroscopy and double‐resonance rotational interrogation) enhance sensitivity and selectivity. These advances have unlocked detailed insight into fundamental reaction pathways, quantum nuclear dynamics, astrochemical species and ligand–ion interactions, with implications spanning interstellar chemistry, precision metrology and the design of tailored catalytic materials.
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Ion Trap Spectroscopy of Molecular Ions publication trend
The graph below shows the total number of articles in ion trap spectroscopy of molecular ions across all publications each year (not limited to Nature Index journals).
Technical terms
Ion trap: A device that confines charged particles using oscillating electric fields, enabling prolonged interrogation under controlled conditions.
Multipole ion trap: A trap geometry employing multiple rods or wires to create a smooth potential well for efficient radio-frequency confinement and low heating rates.
Cryogenic cooling: The reduction of ion translational and internal temperature—often below 10 K—via collisions with a cold buffer gas or refrigerator, minimising spectral broadening.
Action spectroscopy: A method in which photon absorption by an ion leads to a detectable action (fragmentation, fluorescence, motional change), used to infer absorption spectra without direct light transmission measurements.
Leak-out-spectroscopy (LOS): An action technique where vibrational excitation reduces the trapping potential, allowing ions to “leak out” of the trap and be counted as a spectroscopic signal.
Rovibrational transitions: Combined rotational and vibrational energy level changes of a molecule, often probed in the mid-infrared to reveal structural and dynamical information.
Infrared photodissociation (IRPD) spectroscopy: A form of action spectroscopy where IR photon absorption induces bond cleavage or tag loss, yielding band positions and intensities for vibrational analysis.
References
- High-resolution ro-vibrational and rotational spectroscopy of HC 3 O +. Physical Chemistry Chemical Physics (2023).
- High-resolution rovibrational and rotational spectroscopy of the singly deuterated cyclopropenyl cation, c-C 3 H 2 D +. Faraday Discussions (2023).
- Gas-Phase Infrared Action Spectroscopy of CH2Cl+ and CH3ClH+: Likely Protagonists in Chlorine Astrochemistry. Molecules (2024).
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