Cryogenic ion trap vibrational spectroscopy of hydrogen-bonded clusters relevant to atmospheric chemistry

Abstract

Recent advances in the gas phase vibrational spectroscopy of mass-selected ions are described, highlighting experiments on hydrogen-bonded (HBed) clusters relevant to atmospheric chemistry. The use of cryogenic ion traps in combination with the widely tunable and intense radiation from infrared free electron lasers has allowed for new molecular-level insights into the structure and other properties of HBed clusters. Advances and challenges in the interpretation of their vibrational action spectra, in particular, the importance of considering anharmonic effects, are described and discussed. The advantages of isomer-specific measurements relying exclusively on excitations within the vibrational manifold are also evaluated. The article concludes with an outlook on future challenges and perspectives

Identification of Active Sites and Structural Characterization of Reactive Ionic Intermediates by Cryogenic Ion Trap Vibrational Spectroscopy

“…As both dissociation steps can produce fragment ions of identical mass an intermediate mass‐selection stage is required (see Scheme ). Typically, the second laser pulse (hν 2 ) is tuned to an isomer‐specific IR transition, generating an isomer‐specific dissociation signal . The first laser pulse (hν 1 ) is then scanned over the spectral region of interest and only absorptions due to the selected isomer will be picked up in the form of dips in the isomer‐specific dissociation signal.…”

“…The first laser pulse (hν 1 ) is then scanned over the spectral region of interest and only absorptions due to the selected isomer will be picked up in the form of dips in the isomer‐specific dissociation signal. This technique can also be applied in a hole‐burning type of experiment, where hν 1 is kept fix at an isomer‐specific transition and hν 2 is tuned . A simpler version of this technique, corresponding to an IR 2 MS 1 detection scheme, was recently applied by Jašík et al.…”

Atomically resolved phase transition of fullerene cations solvated in helium droplets

“…Tagging of ions with rare gas atoms and in particular with helium (He) provides an elegant method to measure absorption spectra of cold ionic species with minimum disturbing effects of a matrix1234. Very recently, several laboratories developed instruments to master He tagging of complex molecules, which requires cooling of the ions in cryogenic traps56789 or supersonic jets10.…”

Mass spectrometry of aerosol particle analogues in molecular beam experiments

“…On the other hand, such clusters can be investigated in molecular beams. In these experiments, generation and growth of the clusters can be studied and their structure and composition can be revealed in unprecedented details . In addition, different processes can be induced in these clusters by photons, electrons, ions, and other types of radiation with various energies, in analogy to the atmospheric processes triggered by cosmic radiation.…”