Gas-phase vibrational spectroscopy of the dysprosium monoxide molecule and its cation.

Rotationally resolved vibrational spectra of DyO and DyO in a molecular beam are obtained by IR excitation from the X8 ground state and from high- Rydberg states of DyO using an infrared free electron laser. Vibrational excitation is detected either by resonance enhanced multiphoton ionisation from X8( = 1) or by autoionisation of Rydberg states converging to DyO( = 1). For most heavy molecules, the large spectral width of an infrared free electron laser does not allow for rotational resolution.

Structure and Conformation Determine Gas-Phase Infrared Spectra of Detergents.

Native mass spectrometry of membrane proteins relies on non-ionic detergents which protect the protein during transfer from solution into the gas phase. Once in the gas phase, the detergent micelle must be efficiently removed, which is usually achieved by collision-induced dissociation (CID). Recently, infrared multiple photon dissociation (IRMPD) has emerged as an alternative activation method for the analysis of membrane proteins, which has led to a growing interest in detergents that efficiently absorb infrared light.

Infrared action spectroscopy of the deprotonated formic acid trimer, trapped in helium nanodroplets.

Hydrogen bonding interactions are essential in the structural stabilization and physicochemical properties of complex molecular systems, and carboxylic acid functional groups are common participants in these motifs. Consequently, the neutral formic acid (FA) dimer has been extensively investigated in the past, as it represents a useful model system to investigate proton donor-acceptor interactions. The analogous deprotonated dimers, in which two carboxylate groups are bound by a single proton, have also served as informative model systems.

Establishing carbon-carbon double bond position and configuration in unsaturated fatty acids by gas-phase infrared spectroscopy.

Fatty acids are an abundant class of lipids that are characterised by wide structural variation including isomeric diversity arising from the position and configuration of functional groups. Traditional approaches to fatty acid characterisation have combined chromatography and mass spectrometry for a description of the composition of individual fatty acids while infrared (IR) spectroscopy has provided insights into the functional groups and bond configurations at the bulk level. Here we exploit universal 3-pyridylcarbinol ester derivatization of fatty acids to acquire IR spectra of individual lipids as mass-selected gas-phase ions.

Adatom Bonding Sites in a Nickel-Fe O (001) Single-Atom Model Catalyst and O Reactivity Unveiled by Surface Action Spectroscopy with Infrared Free-Electron Laser Light.

Single-atom (SA) catalysis presently receives much attention with its promise to decrease the cost of the active material while increasing the catalyst's performance. However, key details such as the exact location of SA species and their stability are often unclear due to a lack of atomic level information. Here, we show how vibrational spectra measured with surface action spectroscopy (SAS) and density functional theory (DFT) simulations can differentiate between different adatom binding sites and determine the location of Ni and Au single atoms on Fe O (001).

Studying the Key Intermediate of RNA Autohydrolysis by Cryogenic Gas-Phase Infrared Spectroscopy.

Over the course of the COVID-19 pandemic, mRNA-based vaccines have gained tremendous importance. The development and analysis of modified RNA molecules benefit from advanced mass spectrometry and require sufficient understanding of fragmentation processes. Analogous to the degradation of RNA in solution by autohydrolysis, backbone cleavage of RNA strands was equally observed in the gas phase; however, the fragmentation mechanism remained elusive.

Cryogenic infrared spectroscopy provides mechanistic insight into the fragmentation of phospholipid silver adducts.

Tandem mass spectrometry is arguably the most important analytical tool for structure elucidation of lipids and other metabolites. By fragmenting intact lipid ions, valuable structural information such as the lipid class and fatty acyl composition are readily obtainable. The information content of a fragment spectrum can often be increased by the addition of metal cations.

Unveiling Glycerolipid Fragmentation by Cryogenic Infrared Spectroscopy.

Mass spectrometry is routinely employed for structure elucidation of molecules. Structural information can be retrieved from intact molecular ions by fragmentation; however, the interpretation of fragment spectra is often hampered by poor understanding of the underlying dissociation mechanisms. For example, neutral headgroup loss from protonated glycerolipids has been postulated to proceed via an intramolecular ring closure but the mechanism and resulting ring size have never been experimentally confirmed.

Surface oxygen Vacancies on Reduced Co O (100): Superoxide Formation and Ultra-Low-Temperature CO Oxidation.

The activation of molecular oxygen is a fundamental step in almost all catalytic oxidation reactions. We have studied this topic and the role of surface vacancies for Co O (100) films with a synergistic combination of experimental and theoretical methods. We show that the as-prepared surface is B-layer terminated and that mild reduction produces oxygen single and double vacancies in this layer.

Non-covalent double bond sensors for gas-phase infrared spectroscopy of unsaturated fatty acids.

The position and configuration of carbon-carbon double bonds in unsaturated fatty acids is crucial for their biological functions and influences health and disease. However, double bond isomers are not routinely distinguished by classical mass spectrometry workflows. Instead, they require sophisticated analytical approaches usually based on chemical derivatization and/or instrument modification.

Direct Experimental Characterization of the Ferrier Glycosyl Cation in the Gas Phase.

The Ferrier rearrangement reaction is crucial for the synthesis of pharmaceuticals. Although its mechanism was described more than 50 years ago, the structure of the intermediate remains elusive. Two structures have been proposed for this Ferrier glycosyl cation: a 1,2-unsaturated cation that is resonance-stabilized within the pyranose ring or a cation that is stabilized by the anchimeric assistance of a neighboring acetyl group.

Probing the conformational landscape and thermochemistry of DNA dinucleotide anions via helium nanodroplet infrared action spectroscopy.

Isolation of biomolecules in vacuum facilitates characterization of the intramolecular interactions that determine three-dimensional structure, but experimental quantification of conformer thermochemistry remains challenging. Infrared spectroscopy of molecules trapped in helium nanodroplets is a promising methodology for the measurement of thermochemical parameters. When molecules are captured in a helium nanodroplet, the rate of cooling to an equilibrium temperature of ca.

Resolving Sphingolipid Isomers Using Cryogenic Infrared Spectroscopy.

1-Deoxysphingolipids are a recently described class of sphingolipids that have been shown to be associated with several disease states including diabetic and hereditary neuropathy. The identification and characterization of 1-deoxysphingolipids and their metabolites is therefore highly important. However, exact structure determination requires a combination of sophisticated analytical techniques due to the presence of various isomers, such as ketone/alkenol isomers, carbon-carbon double-bond (C=C) isomers and hydroxylation regioisomers.

Elucidating Surface Structure with Action Spectroscopy.

Surface Action Spectroscopy, a vibrational spectroscopy method developed in recent years at the Fritz Haber Institute is employed for structure determination of clean and HO-dosed (111) magnetite surfaces. Surface structural information is revealed by using the microscopic surface vibrations as a fingerprint of the surface structure. Such vibrations involve just the topmost atomic layers, and therefore the structural information is truly surface related.

Surface action spectroscopy with rare gas messenger atoms.

Action spectroscopy with inert gas messengers is commonly used for the characterization of aggregates in the gas phase. The messengers, often rare gas atoms or D molecules, are attached to the gas phase aggregates at low temperature. Vibrational spectra of the aggregates are measured via detection of inert gas desorption following a vibrational excitation by variable-energy infrared light.

Vibrational Spectroscopy of Fluoroformate, FCO, Trapped in Helium Nanodroplets.

Fluoroformate, also known as carbonofluoridate, is an intriguing molecule readily formed by the reductive derivatization of carbon dioxide. In spite of its well-known stability, a detailed structural characterization of the isolated anion has yet to be reported. Presented in this work is the vibrational spectrum of fluoroformate obtained by infrared action spectroscopy of ions trapped in helium nanodroplets, the first application of this technique to a molecular anion.

Vibrational Action Spectroscopy of Solids: New Surface-Sensitive Technique.

Vibrational action spectroscopy employing infrared radiation from a free-electron laser has been successfully used for many years to study the vibrational and structural properties of gas phase aggregates. Despite the high sensitivity of this method no relevant studies have yet been conducted for solid sample surfaces. We have set up an experiment for the application of this method to such targets, using infrared light from the free-electron laser of the Fritz Haber Institute.

Hydrogen Chemisorption on Singly Vanadium-Doped Aluminum Clusters.

The effect of vanadium doping on the hydrogen adsorption capacity of aluminum clusters (Al , n=2-18) is studied experimentally by mass spectrometry and infrared multiple photon dissociation (IRMPD) spectroscopy. We find that vanadium doping enhances the reactivity of the clusters towards hydrogen, albeit in a size-dependent way. IRMPD spectra, which provide a fingerprint of the hydrogen binding geometry, show that H dissociates upon adsorption.

Excess charge driven dissociative hydrogen adsorption on TiO.

The mechanism of dissociative D adsorption on TiO, which serves as a model for an oxygen vacancy on a titania surface, is studied using infrared photodissociation spectroscopy in combination with density functional theory calculations and a recently developed single-component artificial force induced reaction method. TiO readily reacts with D under multiple collision conditions in a gas-filled ion trap held at 16 K forming a global minimum-energy structure (DO-Ti-(O)-Ti(D)-O). The highly exergonic reaction proceeds quasi barrier-free via several intermediate species, involving heterolytic D-bond cleavage followed by D-atom migration.

Glycan Fingerprinting via Cold-Ion Infrared Spectroscopy.

The diversity of stereochemical isomers present in glycans and glycoconjugates poses a formidable challenge for comprehensive structural analysis. Typically, sophisticated mass spectrometry (MS)-based techniques are used in combination with chromatography or ion-mobility separation. However, coexisting structurally similar isomers often render an unambiguous identification impossible.

Dissociative Water Adsorption by AlO in the Gas Phase.

We use cryogenic ion trap vibrational spectroscopy in combination with density functional theory (DFT) to study the adsorption of up to four water molecules on AlO. The infrared photodissociation spectra of [AlO(DO)] are measured in the O-D stretching (3000-2000 cm) as well as the fingerprint spectral region (1300-400 cm) and are assigned based on a comparison with simulated harmonic infrared spectra for global minimum-energy structures obtained with DFT. We find that dissociative water adsorption is favored in all cases.

Gas-Phase Vibrational Spectroscopy of the Aluminum Oxide Anions (Al O ) AlO.

We use cryogenic ion trap vibrational spectroscopy in combination with density functional theory to probe how the structural variability of alumina manifests itself in the structures of the gas-phase clusters (Al O ) AlO with n=1-6. The infrared photodissociation spectra of the D -tagged complexes, measured in the fingerprint spectral range (400-1200 cm ), are rich in spectral features and start approaching the vibrational spectrum of amorphous alumina particles for n>4. Aided by a genetic algorithm, we find a trend towards the formation of irregular structures for larger n, with the exception of n=4, which exhibits a C ground-state structure.

Effects of Charge Transfer on the Adsorption of CO on Small Molybdenum-Doped Platinum Clusters.

The interaction of carbon monoxide with platinum alloy nanoparticles is an important problem in the context of fuel cell catalysis. In this work, molybdenum-doped platinum clusters have been studied in the gas phase to obtain a better understanding of the fundamental nature of the Pt-CO interaction in the presence of a dopant atom. For this purpose, Pt and MoPt (n=3-7) clusters were studied by combined mass spectrometry and density functional theory calculations, making it possible to investigate the effects of molybdenum doping on the reactivity of platinum clusters with CO.