Free-Electron Laser Workshop "Applications of IR Free-Electron Lasers: Latest Developments and Future Directions"

17 Jan 2018, 15:00 → 20 Jan 2018, 10:00 CET

Ringberg Castle

Britta Redlich (FELIX), Gerard Meijer (Fritz-Haber-Institut), Gert von Helden (Fritz-Haber-Institut), Wieland Schöllkopf (Fritz-Haber-Institut)

Applications of IR Free-Electron Lasers:

Latest Developments and Future Directions

Wednesday, 17 January

15:00 → 15:45 Welcome: Wednesday

16:00 → 18:00 Wednesday PM: Wednesday

Convener: Prof. Gerard Meijer (Fritz-Haber-Institut)

16:00 Probing the activation of small molecules by clusters using infrared multiple photon dissociation spectroscopy

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 clusters one can obtain information about the clusters’ structure or the behaviour of adsorbed species. The latter provides valuable insights into the binding geometry, the activation of bonds within the ligands or reactions occurring on the clusters’ surface. Cluster size specific data can be obtained using infrared multiple photon dissociation spectroscopy. To cover the required spectral range from the far to the mid-IR our experiments make use of IR free electron lasers. The talk will discuss exemplary studies on the activation of carbon dioxide by anionic cobalt [2] and rhodium, and platinum clusters and on hydrogen by cationic cobalt clusters.

[1] D.J. Harding, A. Fielicke, Chem. Eur. J. 20 (2014) 3258
[2] A. Yanagimachi, et al. J. Phys. Chem. C 120 (2016) 14209.

Speaker: Dr André Fielicke (Fritz-Haber-Institut, Berlin, Germany)

16:40 Using infrared pre-excitation to induce species-specific electronic excitation

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 UV-Vis pulse follows. If the electronic spectrum exhibits an IR-induced shift, the molecule is brought into resonance with the UV-Vis pulse. The system can be then probed in the electronically excited state in a species-specific manner, e.g. by another IR pulse. In this contribution, two applications of this method called VIPER (Vibrationally Promoted Electronic Resonance) are presented [1]. It is firstly shown that chemical exchange between hydrogen-bonded and free molecular species can be probed on a time scale beyond the vibrational lifetime [1,2], and secondly, that one molecular species in a mixture of near-identical species be pre-selected in order to induce and monitor its photochemistry [3].
[1] L. J. G. W. van Wilderen, A. T. Messmer, and J. Bredenbeck, Angew. Chem. Int. Ed. 53 (10), 2667–2672 (2014).
[2] L. J. G. W. van Wilderen and J. Bredenbeck, Angew. Chem. Int. Ed. 54 (40), 11624–11640 (2015)
[3] D. Kern-Michler, C. Neumann, N. Mielke, L. J. G. W. van Wilderen, M. Reinfelds, J. von Cosel, F. Santoro, A. Heckel, I. Burghardt, and J. Bredenbeck, J. Am. Chem. Soc. doi: 10.1021/jacs.7b08723 (2018).

Speaker: Dr Luuk van Wilderen (Institute of Biophysics, Goethe-Universität, Frankfurt am Main, Germany)

17:20 New infrared ion spectroscopy experiments at FELIX using an ETD enabled ion trap MS

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 capabilities enable detailed investigation of dissociation reaction networks. We show an example for the deamidation reactions of small peptides containing Asn and Gln side chains. The ETD source enables the investigation of the typical ETD generated peptide fragments, especially c- and z-type ions. We address the question of whether radical migration occurs in z-type ions and whether c-type ions reveal details of the ETD reaction mechanism. The ETD source can also be used to induce 1-electron reduction of multiply charged metal-ligand complexes (“ETnoD”). We show that this enables the study of coordination complexes in oxidation states that are otherwise hard to access by ESI ionization and we investigate the structural changes upon reduction of the metal center for different coordination complexes. Finally, very recently, experiments replacing the ESI source with an APCI source have enabled the investigation of non-polar species. We present the first IR spectrum of protonated Buckminster fullerene.

Speaker: Prof. Jos Oomens (FELIX Laboratory, Radboud University, Nijmegen, The Netherlands)

20:00 → 20:40 Wednesday After Dinner: Wednesday

Convener: Prof. Gerard Meijer (Fritz-Haber-Institut)

20:00 Surface Action Spectroscopy with Rare Gas Messenger Atoms

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 solids.
Experiments performed for neon covered V$_2$O$_3$(0001) films on Au(111) show that this method is applicable to surfaces. Rare gas desorption by excitation of surface vibrational modes is probably a single photon process as indicated by experimental observations. In addition to this surface sensitive channel there is also a bulk sensitive channel in which absorption of laser light by a state with a high absorption cross section like a bulk polarition leads to gas desorption induced by sample warming.
Infrared absorption reflection spectroscopy (IRAS) is another commonly used method for the vibrational characterization of surfaces. Surface action spectroscopy has two advantages over this method: (1) a reference spectrum is not required for surface action spectroscopy which means that modification of features by structures in the reference spectrum does not occur and (2) the use of a messenger gas offers the possibility to cover only part of the surface which means that in this case the action spectrum exclusively stems from the covered areas.

Speaker: Dr Helmut Kuhlenbeck (Fritz-Haber-Institut)

Thursday, 18 January

09:00 → 12:30 Thursday AM

Convener: Dr Britta Redlich (FELIX Laboratory, Radboud University)

09:00 TBD

confirmed

Speaker: Prof. Stephan Schlemmer (Universität Köln, Germany)

09:40 Vibrational spectroscopy on metal cluster-molecule complexes in the gas phase

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 mechanism. In addition, for small-sized clusters, ranging from two to a few tens of atoms, direct comparison between experiment and quantum-chemical calculations is possible.
In this talk, I will discuss two examples in which infrared multiple photon dissociation spectroscopy (IRMPD) is used to investigate the interaction of metal clusters with small molecules. First, the adsorption of CO on Mo and Nb doped cationic platinum clusters is studied with the goal to enhance understanding about the CO poisoning effect of Pt catalyst nanoparticles in proton exchange membrane fuel cells. Reactivity measurement in a low-pressure collision cell showed significant reduction in the reactivity of the doped Pt clusters compared to bare Pt clusters, which is attributed to electron transfer from the highly coordinated dopants to the Pt atoms and the concomitant lower CO binding energies [3]. Stretching frequencies of the adsorbed CO molecules reflect dopant-induced charge redistribution within the clusters [4].
Second, I will present a study of hydrogen adsorption on the V and Rh doped cationic aluminum clusters. IRMPD spectra, which provide a fingerprint of the hydrogen binding geometry, prove that H$_2$ dissociates upon adsorption for the V doped clusters. Orbital analysis shows that the activation barriers are due to an unfavorable overlap between cluster and hydrogen orbitals [5]. For Rh doped clusters, depending on the cluster sizes, either the H$_2$ binds dissociatively or it adsorbs molecularly in Kubas complexes. This size dependence is not due to kinetic impediment of the hydrogenation reaction by an activation barrier, but to binding energy differences [6].

[1] D. Justes, R. Mitrić, N. Moore, V. Bonačić-Koutecký, A. Castleman, Jr., J. Am. Chem. Soc. 125, 6289 (2003).
[2] S. M. Lang, T. Bernhardt, R. Barnett, U. Landman, Angew. Chem. Int. Ed. 49, 980 (2010).
[3] P. Ferrari, L.M. Molina, V.E. Kaydashev, J.A. Alonso, P. Lievens, E. Janssens, Angew. Chem. Int. Ed. 55, 11059 (2016).
[4] P. Ferrari, J. Vanbuel, N.M. Tam, M.T. Nguyen, S. Gewinner, W. Schöllkopf, A. Fielicke, E. Janssens, Chem. Eur. J. 23, 4120 (2017).
[5] J. Vanbuel, E.M. Fernández, P. Ferrari, S. Gewinner, W. Schöllkopf, L.C. Balbás, A. Fielicke, E. Janssens, Chem. Eur. J. 23, 15638 (2017).
[6] J. Vanbuel, M.Y. Jia, P. Ferrari, S. Gewinner, W. Schöllkopf, M.T. Nguyen, A. Fielicke, E. Janssens, Top. Catal. (2017). https://doi.org/10.1007/s11244-017-0878-x

Speaker: Prof. Ewald Janssens (KU Leuven, Belgium)

10:20 Coffee

Coffee Break

10:45 Magnetism of clusters as a test for fundamental magnetic problems

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 considerations, is what happens in a system smaller than the length scale of the bulk exchange field?
Here we follow, both experimentally and theoretically, the development of magnetism in very small particles, or clusters, of various materials, starting from the atomic limit and adding one atom at a time. A wealth of non-intuitive and instructive magnetic phenomena can be found. Thus, in rare-earth clusters the usual bulk RKKY exchange interaction is replaced with an oscillatory ferromagnetic double-exchange and antiferromagnetic superexchange [1], leading to irregular oscillations of magnetic order as a function of the cluster size.
The most unusual is the appearance of magnetism in the normally nonmagnetic materials, such as rhodium [2], or even vanadium and niobium [3]. Particularly striking is Rh, that presents an example of multiferroic behavior in metal clusters. The fact that it is observed in rhodium is even more surprising, since this metal is neither ferromagnetic nor ferroelectric in the bulk. From a broader perspective, the emergence of ferroelectricity in small metal clusters appears to be mediated by very low energy excitations, possibly involving a single vibronic mode that is associated with a broken symmetry ground state [2].
Another intriguing question is how a single dopant atom can modify the properties of a cluster? Magnetic deflection experiments on isolated Co doped Nb clusters demonstrate a strong size dependence of magnetic properties, with large magnetic moments in certain cluster sizes, and fully non-magnetic behavior of others. There are in principle two explanations for this behavior. Either the local moment at the Co site is absent or it is screened by the delocalized electrons of the cluster, i.e. the Kondo effect. In order to reveal the physical origin, first, we established the ground state geometry of the clusters by experimentally obtaining their vibrational spectra and comparing them with a density functional theory study. Then, we performed an analysis based on the Anderson impurity model. It appears that the non-magnetic clusters are due to the absence of the local Co moment and not due to the Kondo effect. In addition, the magnetic behavior of the clusters can be understood from an inspection of their electronic structure. Here magnetism is favored when the effective hybridization around the chemical potential is small, while the absence of magnetism is signalled by a large effective hybridization around the chemical potential.
As a final note, the isolation of the clusters from the environment makes them ideal objects to study a transition between quantum and classical behavior. Kramers degeneracy, onset of Kondo screening, etc, could be studied with exact control of the electronic and geometric structure.

The work was supported by de Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) and the European Research Council.

[1] L. Peters et al., Sci. Reports 6, 19676 (2016).
[2] L. Ma et al., Phys. Rev. Lett. 113, 157203 (2014).
[3] A. Diaz Bachs et al., to be published

Speaker: Prof. Andrei Kirilyuk (FELIX Laboratory, Radboud University, Nijmegen, The Netherlands)

11:25 Nonlinear Phonon Spectroscopy using Infrared Free-Electron Lasers

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 examples of nonlinear phonon spectroscopy demonstrating these capabilities: second harmonic phonon spectroscopy, two-photon absorption spectroscopy, and vibrational sum-frequency spectroscopy. Based on these examples, I will discuss the prospect of FEL-based nonlinear solid-state spectroscopy.

Speaker: Dr Alex Paarmann (Fritz-Haber-Institut, Berlin, Germany)

12:05 Intracavity IR multiple-photon dissociation spectroscopy of transition metal carbene cations

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 methane activated by four metal cations [1]. The use of FELICE was deemed crucial, as it was suspected that dissociation via IVR-mediated multiple-photon excitation is hampered by a low IVR relaxation rate associated to a low density of states in these four atom species. Although the spectra obtained allowed for convincing product assignments, they also raised questions about unassigned spectral features, such as possible overtones and exceptionally broad band structures.
We recently re-visited this system employing perdeuterated methane CD$_4$ in an attempt to clarify several observations made. We here present the resulting spectra and a consistent spectral analysis.

[1] Lapoutre, V. J. F.; Redlich, B.; van der Meer, A. F. G.; Oomens, J.; Bakker, J. M.; Sweeney, A.; Mookherjee, A.; Armentrout, P. B. Structures of the Dehydrogenation Products of Methane Activation by 5d Transition Metal Cations. J. Phys. Chem. A 117 (20), 4115–4126 (2013).

Speaker: Dr Joost Bakker (FELIX Laboratory, Radboud University, Nijmegen, The Netherlands)

14:00 → 16:00 Hike

Hike (if weather conditions permit)

16:00 → 18:00 Thursday PM

Convener: Dr André Fielicke

16:00 Coffee

Coffee Break

16:15 Anomalous response of graphene to far-infrared radiation

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. linear response –, but also affect the transport in graphene – i.e. nonlinear effects – already for very low field strengths.

We further show that this highly nonlinear response can be used for efficient optical harmonics generation – the multiplication of the photon energy as a result of nonlinear light-matter interaction. We report on the generation of THz harmonics in single-layer graphene under ambient conditions, driven by THz fields on the order of only 10s of kV/cm, and with the field conversion efficiencies as high as $\sim10^{-3}$ and $\sim10^{-4}$ for the third and fifth THz harmonics, respectively. The effective THz nonlinear optical coefficients of graphene χ$^{(3)}$ exceeds that of typical solids by 10 orders of magnitude. The enormousness of the nonlinear optical response can be traced to a fundamentally different origin of the nonlinearity.

Speaker: Prof. Mischa Bonn (Max Planck Institute for Polymer Research, Mainz, Germany)

16:55 Analytical ion spectroscopy: a new route to biomarker discovery in metabolomics

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 spectroscopy of mass-selected ions. This approach provides information on functional groups in an unknown and has the potential for reference compound free identification in combination with theoretically predicted IR spectra.
In a first example, we focus on the differentiation of N-acetylmannosamine, a recently discovered biomarker for NANS-deficiency, a new inborn error of metabolism in sialic acid metabolism, from other possible enantiomeric N-acetylhexosamines found at the same m/z. This differentiation is not possible using standard operating HPLC-MS/MS protocols in most bioanalytical laboratories, as the enantiomers cannot be separated using reversed-phase chromatography and have identical MS/MS fragmentation spectra. Here, we demonstrate the use of IR ion spectroscopy to cleanly distinguish three N-acetylhexosamines directly from urine and cerebrospinal fluid (CSF) without any sample preparation (aside from dilution) or chromatographic separation.
In a second example, we use high-performance liquid chromatography in combination with IR ion spectroscopy for the identification of positional isomers of hydroxy-atorvastatins, the primary metabolites of the drug atorvastatin (lipitor).
Human diseases often have the potential to be detected by the identification of a single molecular species present in a patient body fluid. The majority of metabolomics laboratories rely on mass spectrometry to identify the presence of abnormal levels of specific small molecules in common body fluids that correlate with diseases, drug treatments, and environmental factors. However, the field is faced with a rapidly increasing number of known metabolic diseases for which these standard laboratory analytical techniques often fail to provide a definitive identification. In a final example, we have used IR ion spectroscopy to partially identify a previously detected but yet unidentified biomarker of the metabolic disease known as antiquitin deficiency. This peak “X” is thought to be associated with symptoms of intellectual disability that persist despite current treatments.

Speaker: Dr Jonathan Martens (FELIX Laboratory, Radboud University, Nijmegen, The Netherlands)

17:35 Atomic-scale heterostructures studied with mid-IR second-harmonic phonon spectroscopy

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 nonlinear optical response of an AlN/GaN superlattice with varying layer thicknesses from 2 nm to 4 nm independently for both constituent materials by means of second-harmonic phonon spectroscopy using the FHI free-electron laser. The improved spectral resolution of the second-harmonic spectra compared to linear measurements allows for unique assignment of peaks to specific XH modes as well as a demonstration of their tunability based on the constituents' layer thicknesses.

Speaker: Christopher Winta (Fritz-Haber-Institut der MPG)

20:00 → 21:00 Thursday After Dinner: Poster Session

Friday, 19 January

09:00 → 12:30 Friday AM: Friday

Convener: Prof. Gert von Helden (Fritz-Haber-Institut der Max-Planck-Gesellschaft)

09:00 Differential Mobility separation and IRMPD identification of amino acids and isomers

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 species. In this context, ion mobility spectrometry represents an interesting alternative, or complementary approach, to condensed phase chromatography which require pre- or post-column derivatization.
We propose here to investigate the performance of differential ion mobility spectrometry (DIMS) coupled to tandem mass-spectrometry for the separation of the 20 common AA. With the exception of Leucine/Isoleucine, all pairs of AA can be separated using N$_2$ as a carrier gas. Peak-to-peak resolution for each pairwise combination of AA ions are systematically derived for electric field strength values, and it turns out that ~80% can be baseline separated.
The potential of the DIMS-MS/MS experiment in combination to infrared activation is also presented for the separation and identification of sarcosine, a biomarker candidate of prostate cancer, from isomers. Baseline separation of protonated sarcosine from alpha- and beta-alanine isomers can be easily achieved using only N$_2$ as carrier gas. Identification of DIMS peak is performed using an isomer specific activation mode, where DIMS- and mass-selected ions are irradiated at selected wavenumbers allowing for the specific fragmentation through an infrared multiple photon dissociation (IRMPD) process. Based on the comparison of IR spectra of the three isomers, we show that specific depletion of the two protonated alpha- and beta-alanine can be achieved, thus allowing for clear identification of the sarcosine peak. It is also demonstrated that DIMS-MS/MS(IRMPD) spectra in the carboxylic C=O stretching region allows for the resolution of overlapping peaks.

Speaker: Prof. Philippe Maître (Université Paris Sud, Orsay, France)

09:40 Geometric and Electronic Structure of Flavins

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 mononucleotide (FMN, co-enzyme), and flavin adenosine dinucleotide (FAD, flavo-protein). Their diverse photochemical properties arising from the LC chromophore make them of fundamental importance for many biological systems and phenomena. Their relevance was acknowledged by the Nobel Prize in Chemistry awarded to Paul Karrer in 1937 for his work on flavins and vitamins. Flavins absorb in a wide spectral range from the optical to the UV region, and their optical and photochemical properties vary sensitively with their oxidation, protonation, metalation, and solvation state. Despite their importance, prior to our work, flavins have not been characterized in the gas phase to determine their intrinsic properties. To this end, we systematically characterized the geometric structure of protonated and metalated flavins (X+Fl, X=H, Li-Cs, Cu-Au) by IRMPD spectroscopy at room temperature in a FT-ICR mass spectrometer coupled to the IR free electron laser FELIX [1-3]. Comparison of the IRMPD spectra recorded in the fingerprint range with DFT calculations allows for establishing the preferred protonation and metalation sites, the interaction strength, and the type of bonding. In a second step, we utilized a recently commissioned cryogenic ion trap spectrometer (BerlinTrap) [4] to record first optical spectra of H+Fl and M+Fl at low temperature (T=20 K) to probe their complex electronic structure arising from the rich manifold of excited states with ππ and nπ character [4,5]. The analysis of these spectra is accomplished by TD-DFT calculations coupled to Franck-Condon simulations, providing detailed insight into the excited state properties.

[1] J. Langer, A. Günther, S. Seidenbecher, G. Berden, J. Oomens, O. Dopfer, Chem. Phys. Chem. 15, 2550 (2014).
[2] A. Günther, P. Nieto, G. Berden, J. Oomens, O. Dopfer, Phys. Chem. Chem. Phys. 16, 14161 (2014).
[3] P. Nieto, A. Günther, G. Berden, J. Oomens, O. Dopfer, J. Phys. Chem. A 120, 8297 (2016).
[4] A. Günther, P. Nieto, D. Müller, A. Sheldrick, D. Gerlich, O. Dopfer, J. Mol. Spectrosc. 332, 8 (2017).
[5] A. Sheldrick, D. Müller, A. Günther, P. Nieto, O. Dopfer, Chem. Eur. J., submitted (2018).

Speaker: Prof. Otto Dopfer (TU Berlin, Germany)

10:20 Coffee

Coffee break

10:45 Resonant two-color IR-IR photodissociation (R2PD) of cryogenically cooled ion-molecule complexes

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 establish the ground state spectra of cold complexes with the messenger tagging technique. Then we fix the pump laser frequency to one of these transitions in the bare complex and scan the probe laser to obtain the photodissociation spectrum of the upper level populated by the pump. Scanning both IR lasers then yields a two-dimensional map (below) of the level structure in the energy region close to, and far above the dissociation threshold. The method is essentially a cluster variation of the vibrationally-mediated photodissociation experiments pioneered in the 1990s by Crim and Rizzo on polyatomic molecules. In the cluster regime, we find long lived (>50 microseconds!) vibrational levels hundreds of wavenumbers above the dissociation threshold (D$_0$), and surprisingly localized excitations for the bound OH stretches very close to D$_0$. This behavior allows us to follow many pathways up the vibrational landscape far beyond the dissociation limit, and points to a new class of FEL experiments that can establish the anharmonicities of soft modes in complexes prepared just below the dissociation threshold.

Speaker: Prof. Mark Johnson (Yale University, New Haven, CT, USA)

11:25 Commission and the First Experiment of Dalian Coherent Light Source

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 (DCLS) delivers optical beam in the 50-180 nm region in picoseconds or 100 femtoseconds for such research. High gain harmonic generation (HGHG) is the perfect choice in FEL for narrow bandwidth, stable power and low cost due to fewer undulators. After eight months of installation and machine commissioning, a 300-MeV electron beam was achieved with peak current of more than 300A, and the emittance was less than 1.5 mm.mrad. The VUV-FEL power for individual pulse at 133 nm approached more than 200 microJoules with 266 nm seed laser in January, 2017. The gain curve and spectrum of HGHG & SASE FEL was measured, and tapering undulator helps increase the power by almost 100% when the FEL output saturated. The user experiment started in June, 2017. It is open for good proposals from the whole world. In this talk, I will present the commission, main specifications, and the first experiment of Dalian Coherent Light Source.

Speaker: Prof. Ling Jiang (Dalian Institute of Chemical Physics, Chinese Academy of Sciences, China)

12:05 Enantiomer-specific spectroscopy and coherent population enrichment of chiral molecules

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 modern microwave spectroscopy techniques, where we can apply microwave radiation of arbitrary polarization. This has recently allowed us to demonstrate enantiomer-specific rotational state transfer of chiral molecules [1]. This new technique is building on previous experiments on sensitive chiral analysis via microwave three-wave mixing [2]. The method selectively promotes either left or right handed chiral molecules to a higher rotational state by phase-controlled microwave pulses that drive electric-dipole allowed rotational transitions. It has the potential to pave the way to future experiments with chiral molecules both to test fundamental physical effects such as parity violation effects as well as applications in chemical physics. I will discuss current experimental progress as well as future perspectives.
References
[1] S. Eibenberger, J. Doyle, and D. Patterson. Phys. Rev. Lett. 118, 123002 (2017).
[2] G. K. Drayna, K. Wang, C. Hallas, S. Domingos, S. Eibenberger, J. M. Doyle, D. Patterson. Angew. Chem. Int. Ed. 55, 4957 (2016).
[3] D. Patterson, M. Schnell, and J. M. Doyle. Nature 497, 475–477 (2013).

Speaker: Dr Sandra Eibenberger (Fritz-Haber-Institut der Max-Planck-Gesellschaft)

14:00 → 18:00 Friday PM: Friday

Convener: Dr Wieland Schöllkopf (Fritz-Haber-Institut)

14:00 Recent Advances in Cryogenic Ion Trap Vibrational Spectroscopy

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 necessary, and as a function of the cluster temperature. Recent advances are discussed, including (i) the characterization of methane activation by isomorphically-substituted binary (Al/Fe) metal oxide clusters, (ii) the identification of hydrogen-bond stretching vibrations in protonated water clusters and (iii) coupling microfluidics with infrared photodissociation spectroscopy.

Speaker: Prof. Knut Asmis (Wilhelm-Ostwald-Institut, Universität Leipzig, Germany)

14:40 Infrared Spectroscopy of Ions Trapped in Helium Nanodroplets

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 beam through an ion trap. This experimental approach can be utilized to capture both cationic and anionic molecules ranging in size from tens of Da to several kDa and subsequently probe their structure utilizing vibrational spectroscopy.
To obtain an infrared spectrum of ions in helium nanodroplets, the droplets are irradiated with infrared photons, and the sequential absorption of multiple resonant photons results in evaporation of helium and the production of bare ions. These ions are detected by time-of-flight mass spectrometry, and the infrared spectrum is obtained as the ion signal as a function of the incident photon energy.
This presentation will provide an overview of the experimental methodology as well as the latest application of the technique to both large biomolecules and small model carboxylate systems. Special emphasis will be given to vibrational spectroscopy of carboxylate proton-bound dimers, which exhibit highly anharmonic vibrational transitions in the far-infrared (400-1000 cm$^{−1}$), and fluoroformate, a simple example of reductive derivatization of carbon dioxide that possesses in its infrared spectrum two doublets resulting from Fermi resonance.

Speaker: Dr Daniel Thomas (Fritz-Haber-Institut, Berlin, Germany)

15:45 Coffee

Coffe break

16:15 Slow electron velocity-map imaging and infrared photodissociation spectroscopy of cryogenically cooled anions

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.

Speaker: Prof. Daniel Neumark (UC Berkeley and Lawrence Berkeley National Lab, USA)

16:55 Rotational and vibrational spectroscopy of reactive hydrocarbon cations in a cryogenic ion trap

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 absorption spectroscopy has in the past been successfully applied for spectroscopic studies of molecular ions, but is often hampered by low number densities and spectral congestion due to the multitude of species produced at high excitation energies during their formation process. These limitations can be overcome by performing experiments on mass-selected ions in cryogenic ion trap instruments.

Here I will present first laboratory data on the gas phase spectra of several astrophysically important hydrocarbon cations ranging in size from comparatively small systems (e.g., C$_2$H$^+$, C$_3$H$_2^+$, and C$_3$H$^+$) to PAH cations, made possible by our recent development of sensitive methods for vibrational and rotational action spectroscopy in cryogenic ion traps [1-4]. Details of broadband infrared experiments using the unique combination of a cryogenic ion trap instrument interfaced to the free electron lasers at the FELIX Laboratory, as well as of complementary high-resolution studies using narrow-band continuous-wave radiation sources will be given.

[1] S. Brünken, L. Kluge, A. Stoffels, O. Asvany, and S. Schlemmer, Astrophys. J. Lett., 783, L4 (2014).
[2] O. Asvany, S. Brünken, L. Kluge, and S. Schlemmer, Appl. Phys. B, 114, 203 (2014).
[3] O. Asvany, K.M.T. Yamada, S Brünken, A. Potapov, and S. Schlemmer, Science, 347, 1346 (2015).
[4] S. Brünken, L. Kluge, A. Stoffels, J. Pèrez-Rios, and S. Schlemmer, J. Mol. Spectrosc., 332, 67 (2017).

Speaker: Prof. Sandra Brünken (FELIX Laboratory, Radboud University, Nijmegen, The Netherlands)

17:35 Glycan Fingerprinting via Cold-Ion Infrared Spectroscopy: Method and Application

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 mobility-mass spectrometry. Gas-phase infrared (IR) spectroscopic methods, on the other hand, were limited to smaller glycans due to poor spectral resolution that results from their conformational flexibility and thermal activation during photon absorption.

Here, we overcome this limitation by using cold-ion spectroscopy. The optical signatures of complex carbohydrates in superfluid helium nanodroplets proved to contain a wealth of well-resolved absorption features. Even minute structural variations result in remarkable spectral differences providing the basis for an identification of glycans using their spectral fingerprints.

This presentation covers both the framework of this method as well as first results investigating the physical properties of isolated glycans.

Speaker: Mr Eike Mucha (Fritz-Haber-Institut der Max-Planck-Gesellschaft)

20:00 → 21:00 Friday After Dinner: Round Table Discussion