Laboratory Astrophysics

Rotational action spectroscopy is an experimental method in which rotational spectra of molecules, typically in the microwave to sub-mm-wave domain of the electromagnetic spectrum (B1–1000 GHz), are recorded by action spectroscopy. Action spectroscopy means that the spectrum is recorded not by detecting the absorption of light by the molecules, but by the action of the light on the molecules, e.g., photon-induced dissociation of a chemical bond, a photon-triggered reaction, or photodetachment of an electron. Typically, such experiments are performed on molecular ions, which can be well controlled and mass-selected by guiding and storage techniques. Though coming with many advantages, the application of action schemes to rotational spectroscopy was hampered for a long time by the small energy content of a corresponding photon. Therefore, the first rotational action spectroscopic methods emerged only about one decade ago. Today, there exists a toolbox full of different rotational action spectroscopic schemes which are summarized in this review.

DOI: 10.1039/d1cp03975j

Molecular ions have long been considered key intermediates in the evolution of molecular complexity in the interstellar medium. However, owing to their reactivity and transient nature, ions have historically proved challenging to study in terrestrial laboratory experiments. In turn, their detection and characterization in space is often contingent upon advances in the laboratory spectroscopic techniques used to measure their spectra. In this Review, we discuss the advances over the past 50 years in laboratory methodologies for producing molecular ions and probing their rotational, vibrational and electronic spectra. We largely focus this discussion around the widespread H₃⁺ cation and the ionic products originating from its reaction with carbon atoms. Finally, we discuss the current frontiers in this research and the technical advances required to address the spectroscopic challenges that they represent.

Nature Reviews Physics

The low-frequency stretching and bending vibrations of the isotopologues  and  have been recorded at low temperature and low resolution. For this, a cryogenic 22-pole trapping machine coupled to an IR beamline of the FELIX free electron laser facility has been used. To record the overview spectra, the laser induced reactions have been applied for these species. As this scheme is not applicable to , the latter has been tagged with He and subsequently dissociated by the IR beam. For the resulting - spectrum, broad features are observed below 1000 possibly related to vibrational motions involving the He atom. The extracted vibrational band positions for all species are compared to results from high-level quantum-chemical calculations.

https://doi.org/10.1016/j.jms.2018.02.006

C–H stretches of the fundamental ions CH⁺ and ¹³CH⁺, which have long been searched for, have been observed for the first time in the laboratory. The state-dependent attachment of He atoms to these ions at cryogenic temperatures has been exploited to obtain high-resolution rovibrational data. In addition, the lowest rotational transitions of CH⁺, ¹³CH⁺ and CD⁺ have been revisited and their rest frequency values have improved substantially.

https://doi.org/10.3847/1538-4357/aab36a

C–H stretches of the fundamental ions CH⁺ and ¹³CH⁺, which have long been searched for, have been observed for the first time in the laboratory. The state-dependent attachment of He atoms to these ions at cryogenic temperatures has been exploited to obtain high-resolution rovibrational data. In addition, the lowest rotational transitions of CH⁺, ¹³CH⁺ and CD⁺ have been revisited and their rest frequency values have improved substantially.

https://doi.org/10.3847/1538-4357/aab36a

We report rest frequencies for rotational transitions of the deuterated ammonium isotopologues NH₃D⁺, NH₂D₂⁺, and NHD₃⁺, measured in a cryogenic ion trap machine. For the symmetric tops NH₃D⁺ and NHD₃⁺, one and three transitions are detected, respectively, and five transitions are detected for the asymmetric top NH₂D₂⁺. While the lowest frequency transition of NH₃D⁺ was already known in the laboratory and space, this work enables the future radio astronomical detection of the two other isotopologues.

https://doi.org/10.3847/1538-4357/aadf83

We report rest frequencies for rotational transitions of the deuterated ammonium isotopologues NH₃D⁺, NH₂D₂⁺, and NHD₃⁺, measured in a cryogenic ion trap machine. For the symmetric tops NH₃D⁺ and NHD₃⁺, one and three transitions are detected, respectively, and five transitions are detected for the asymmetric top NH₂D₂⁺. While the lowest frequency transition of NH₃D⁺ was already known in the laboratory and space, this work enables the future radio astronomical detection of the two other isotopologues.

https://doi.org/10.3847/1538-4357/aadf83

Laboratory spectroscopic data of large and complex molecules are of upmost importance for the astronomy community to detect new molecular species in space and to achieve a greater understanding of the chemistry involved in star forming regions and processes. In our publication we present high-resolution rotational spectroscopy of the two higher energy conformers of 2- cyanobutane (C4H9CN), a a member of a larger family of cyanides.

https://doi.org/10.1016/j.jms.2018.11.009

Laboratory spectroscopic data of large and complex molecules are of upmost importance for the astronomy community to detect new molecular species in space and to achieve a greater understanding of the chemistry involved in star forming regions and processes. In our publication we present high-resolution rotational spectroscopy of the two higher energy conformers of 2- cyanobutane (C4H9CN), a a member of a larger family of cyanides.

https://doi.org/10.1016/j.jms.2018.11.009