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New infrared action spectroscopy tool for neutral gas-phase molecules

Date of news: 12 September 2016

Infrared spectroscopy is an efficient tool for the structural analysis of (bio)molecules, especially when experiments are performed in a cooled gas phase environment and combined with theoretical quantum-chemical calculations. This article demonstrates a new infrared spectroscopy technique, which significantly extends the scope of the molecules that can be studied in the gas phase. It is particularly suitable for neutral peptide molecules lacking an ultra-violet (UV) chromophore.

The proposed technique measures infrared spectra of gas-phase molecules cooled down to cryogenic temperatures (below −150 °C), by letting them interact with intense radiation from the free-electron laser FELIX. If the wavelength of FELIX radiation matches one of the infrared transitions, the molecule absorbs multiple infrared photons. In this way, the molecule is heated until it breaks apart (dissociates). The products of the dissociation are probed with a vacuum ultra-violet (VUV) ionizing laser. Subsequently, the infrared spectra are recorded by scanning the wavelength of FELIX and monitoring the intensity of the ionized dissociation products.

Scheme IR action spectroscopy

The demonstrated technique also enables infrared spectroscopy of molecular complexes: several molecules bound together by means of weak interactions such as hydrogen bonding. This creates unique opportunities to selectively study the interactions that are responsible for the structure of the (bio)molecules, either originating from intrinsic molecular properties, or from the surrounding environment.

The authors believe that the demonstrated technique will significantly advance the field of structural studies of molecules and molecular complexes. Such studies are, for example, very important for elucidation of the relationship between the structure of biomolecules and their functions. This knowledge can help to treat certain diseases associated with faulty structural arrangement of protein molecules, for example Alzheimer’s and Parkinson’s disease.


Infrared Action Spectroscopy of Low-Temperature Neutral Gas-phase Molecules of Arbitrary Structure
Vasyl Yatsyna, Daniël J. Bakker, Peter Salén, Raimund Feifel, Anouk M. Rijs and Vitali Zhaunerchyk
Physical Review Letters, September 2016; DOI http://dx.doi.org/10.1103/PhysRevLett.117.118101