Transition metal clusters are frequently used as model systems for low coordinated sites of extended surfaces and their study can provide valuable insights into the mechanisms of surface reactions. In many cases, however, there is still a lack of information on their structures and the relationship between structure and chemical behaviour [1]. Using vibrational spectroscopy of gas-phase...
In solution and at room temperature, UV-Vis spectra of similar molecules are generally broad, strongly overlapping, and barely distinguishable. IR spectra, on the other hand, typically show species-specific features. This specificity is exploited by vibrationally exciting one species with a narrow band (10 – 20 cm$^{-1}$) IR pulsed laser. During the vibrational lifetime, a second non-resonant...
The installation at FELIX of a new quadrupole ion trap mass spectrometer (Bruker Amazon ETD) equipped with extensive MS/MS capabilities including Electron Transfer Dissociation (ETD) has opened new venues in the spectroscopic exploration of ion chemistry. We will give an overview of a number of recent, partially unpublished results. The sensitive ion source and the extensive MS/MS and MSn...
Action spectroscopy with rare gas messenger atoms is commonly used for the characterization of aggregates in the gas phase. With this method vibrational spectra of clusters are measured via detection of rare gas desorption following a vibrational excitation. We have constructed an apparatus for the application of action spectroscopy with rare gas messenger atoms to surfaces of...
Small clusters in the gas phase are ideal model systems for investigating the fundamental aspects of complex reactions [1,2]. The good control over cluster size, composition, and charge state allows distinguishing the effects of these parameters on the studied reactions. In the high-vacuum conditions of a gas-phase experiment there are no contaminating agents that could affect the reaction...
Magnetism is a macroscopic phenomenon that at microscopic level occurs due to exchange interactions, whose typical range, or more simply length scale, is determined by the spatial extent of the quantum mechanical wavefunctions. Confinement of these wavefunctions by for example the presence of a surface leads to many unusual magnetic phenomena. A natural question, in light of these...
The immense spectral brightness of infrared free-electron lasers is ideally suited to resonantly drive large magnitude lattice vibrations in dielectric crystals. In particular for optical phonons, their many ps-long life times result in sharp spectral resonances in the mid- to far-infrared, perfectly matching the tuning range and narrow bandwidth of IR-FELs. In this talk, I will give several...
Methane, a key fossil fuel, is difficult to transport and difficult to convert to other energy rich chemicals because of the strong CH bond; however, several third-row metal cations readily activate methane to form MCH$_2^+$, a metal carbene, and H$_2$.
In a 2013 spectroscopic investigation using the FELICE intracavity free-electron laser, we have been able to identify product structures of...
The outstanding charge transport properties of graphene enable numerous electronic applications of this remarkable material, many of which are expected to operate at ultrahigh, terahertz (THz) rates. In many of these applications, charge carriers in graphene are therefore exposed to very short field transients. Here we show that these THz transients do not only induce charge transport – i.e....
Small molecule identification is a core challenge in various areas of (bio)analytical science, including metabolomics and drug development. We present several examples demonstrating the direct applicability of infrared (IR) ion spectroscopy in the fields of drug metabolism and metabolomics. We present developments that combine separation by high performance liquid chromatography with IR...
Combining multiple atomic-scale layers of polar crystals allows for active modification of phonon frequencies, lifetimes, and hence engineering of the dielectric response. Specifically, new hybrid optical phonon modes emerge in these so-called crystalline hybrids (XHs) due to the modification of chemical bonds at the interfaces and confinement effects.
In our experiments, we study the...
Common amino acids (AA) and their catabolic derivatives have been shown to constitute a class of biomarkers for early diagnosis of diseases such as cancers. In the frame of metabolomics techniques based on tandem mass spectrometry, different strategies can be employed for the separation step, in order to minimize the chemical noise and contribute to the resolution of isobaric or isomeric...
In addition to DNA/RNA and amino acids (proteins), flavins are an important class of biomolecules. Flavins (Fl) are derived from the 7,8-dimethyl-10-alkylisoalloxazine chromophore, which differ by their substituent R at the N10 position. The most important examples of the flavin family are lumichrome (LC, R=H), lumiflavin (LF, R=CH$_3$), riboflavin (RF, vitamin B2, R=ribityl), flavin...
Two-step photoexcitation of cryogenically cooled ion-hydrate clusters provides a way to obtain tag-free spectra of cold ions as well as a new window into the intracluster energy relaxation dynamics that drive predissociation. This is accomplished by recording the photodissociation spectra of individual excited vibrational levels using two-color, two-photon IR-IR photoexcitation. We first...
A Free Electron Laser (FEL) with high brightness, ultrafast laser pulses in the vacuum ultraviolet (VUV) wavelength region is an ideal light source for the excitation of valence electrons and the ionization of molecular systems with very high efficiency. It is quite helpful for studies of important dynamic processes in physical, chemical and biological systems. Dalian Coherent Light Source...
Chiral molecules play a fundamental role in a large variety of biological and chemical processes and their reactions may differ vastly for different enantiomers. Cold, polyatomic molecules offer a plethora of possibilities to test fundamental physics, for quantum control, and for studies of molecular structure, dynamics and cold chemistry. In our experiments we combine buffer gas cooling with...
Cryogenic ion trap vibrational spectroscopy is arguably one of the most powerful and widely applicable structural characterization tools for mass-selected clusters in the gas phase. Combined with the intense and widely tunable radiation from an infrared (IR) free electron laser it allows measuring vibrational spectra over nearly the complete IR spectral range, isomer-specifically, when...
Helium nanodroplets provide an ideal environment for vibrational spectroscopy due to their extremely low equilibrium temperature ($\sim0.4$ K) and minimal matrix-induced spectral perturbation. Whereas the capture of a neutral molecule in a nanodroplet is accomplished using a pickup cham-ber containing analyte vapor, ions can be captured in helium nanodroplets by instead directing a nanodroplet...
Slow electron velocity-map imaging and infrared photodissociation spectroscopy of cryogenically cooled anions are complementary experimental methods that yield vibrationally resolved spectra of complex molecular species. Results from both techniques will be presented, with special emphasis on bare and complexed metal oxide clusters.
Hydrocarbon ions play an important role in combustion and plasma processes, and in the chemistry of planetary atmospheres and the interstellar medium. Laboratory spectroscopic studies of these essential reaction intermediates give valuable insights on their geometrical and electronic structure, and provide accurate transition frequencies needed for their identification in space. Conventional...
The immense structural diversity of carbohydrates enables them to convey key-roles in virtually every biological process. However, this structural diversity, at the same moment, poses a formidable challenge for the analysis. The identification of a complex oligosaccharide typically relies on highly sophisticated mass spectrometry-based techniques, chemical derivatization or, most recently, ion...
