Abstracts -SNSS Seminar on Neutron Spectroscopy

Abstracts -SNSS Seminar on Neutron Spectroscopy

 SNSS Seminar on Neutron Spectroscopy 

At SNSS we aim to strengthen our community by fostering new collaborations and showcasing the excellent science already taking place. Our ongoing seminar series focuses on the science facilitated by the first ESS beamlines, to highlight the existing strengths with the national and international communities and initiate collaborations for the future. 

On November 16 at 13.00-15.00 our fifth seminar will take place and focus on neutron spectroscopy. The seminar will be held on zoom and the program is featured by a mix of internationally established experts as well as young, early career, scientists in neutron spectroscopy. The speakers and abstracts for the seminar are: 

13.05 – 13.35. Dr. Stewart Parker, Instrument Scientist at the ISIS Neutron Facility, U.K. 

Inelastic neutron scattering and its applications. – In this talk, I will give a brief introduction to neutron scattering in general and then discuss inelastic neutron scattering (vibrational spectroscopy with neutrons, INS) in more detail. Using examples from molecular spectroscopy, hydrogen storage materials and catalysis, I will illustrate how the unique capabilities of INS can be used to observe vibrational modes that are inaccessible to infrared and Raman spectroscopy, distinguish fundamentals from higher order transitions and quantify the amount and type of hydrogen present in, or on, a material. 

13.35 – 13.55. MSc. Elisabetta Nocerino, PhD student at Royal Institute of Technology, Sweden 

First experimental observation of vibrational excitations in the Charge Density Wave Superconductor LaPt2Si2 studied with Inelastic Neutron Scattering. – One of the grand challenges in condensed matter physics is the understanding of the mechanisms underlying high temperature superconductivity (SC). Materials with competing electron spectrum instabilities, such as Cooper pairing and charge/spin-density waves (CDW/SDW), represent the ideal playground for this kind of investigations since the particular electron-phonon coupling established in such systems is believed to be a key factor in inducing SC. The quasi-2D Pt-based rare earth intermetallic material LaPt2Si2 belongs to this family of compounds as it exhibits strong interplay between CDW and SC. In this study we present the first experimental observation of the phonon spectra in this material, which clarified some of the open questions coming from the contradictory and sometimes cryptic published literature around LaPt2Si2. 

13.55 – 14.15. Dr. Mikael Andersson, Postdoctoral Researcher at Uppsala University, Sweden 

Why use QENS to study reorientational dynamics – Examples from a few borohydride compounds. – Quasielastic neutron scattering (QENS) can be a powerful tool for studying both local and long-range diffusion in various compounds. In this talk I will discuss how QENS can be used to study the reorientational dynamics of the hydrogen containing polyatomic ions in two borohydrides compounds, silica-NaCB11H12 nanocomposites and NH4BH4, and why this is of interest. The high-temperature phase of NaCB11H12 is known for exhibiting exceptionally high Na-cation conductivity, however upon cooling to room temperature NaCB11H12 undergoes a phase transition to its poorly conducting low temperature phase. The high Na-conductivity has been shown to be linked to the rapidly reorientations of the [CB11H12]- anion which occurs only in the high-temperature phase. Using QENS my colleagues and I showed that by forming a silica-NaCB11H12 nanocomposite the fast reorientational dynamics and the high Na-conductivity persist down to at least 250 K. NH4BH4 is built up by two tetrahedral ions, NH4+ and BH4- arranged in NaCl structure. Both ions are dynamically active on QENS timescales making NH4BH4 a suitable compound for studying the interplay between the reorientational dynamics of two ions with similar geometries and coordination environments. Using QENS it was found that the NH4+ reorientations are significantly faster than the BH4- reorientations. Due to the significantly slower reorientations of the BH4- anion, which appears static to the NH4+ cation, the NH4+ cation experiences a local non-cubic environment which influences its reorientational dynamics. On the other hand the BH4- anion perceives the NH4+ cation as mostly spherical and thus adopts a reorientational motion akin to the octahedral coordination environment imposed by the NaCl structure. 

14.15 – 14.35. Dr. Monika Hartl, Instrument Scientist at the European Spallation Source, Sweden 

Ortho- and parahydrogen conversion observed with optical and neutron vibrational spectroscopy. -Neutron Vibrational Spectoscopy (NVS) has become an important tool for research areas when optical spectroscopy cannot be used. This technique allows for example the characterization of active species and intermediates adsorbed on catalyst surfaces of optically opaque samples. Due to the enhanced sensitivity of NVS to hydrogen, most of the studies involve hydrogenated species and intermediates. Thanks to the increased flux of neutron sources such as the SNS (US), ISIS (UK) and in the future ESS (Sweden), non-hydrogenated samples (e.g. CO2, COx, NOx) are now also being investigated with NVS. This talk will focus on the catalytic conversion of orthohydrogen to parahydrogen at liquid hydrogen temperatures with the aid of vibrational spectroscopy using optical light (Raman) and neutrons (NVS). The results achieved with both techniques will show the complementarity of both techniques. 

14.35 – 14.55. Prof. Jan Swenson, Chalmers University of Technology, Sweden 

Understanding the role of sugars for protein stabilization by neutron scattering. – Proteins are an important component in many medical and food products, and the long-time properties of these products are directly dependent on the stability of their proteins. To enhance this stability it has become common to add disaccharides in general, and trehalose in particular. However, the mechanisms by which disaccharides stabilize proteins and other biological materials are still not fully understood, and therefore we have used neutron diffraction and quasielastic neutron scattering (QENS) in combination of molecular modeling to investigate the stabilizing role of the disaccharides trehalose and sucrose on myoglobin. Our aim was to enhance the general understanding of the role of disaccharides and to obtain specific insights into why trehalose exhibits extraordinary stabilizing properties. The diffraction results show that both disaccharides are preferentially excluded from the protein surface, but that this effect is more pronounced for trehalose than sucrose. Hence, the disaccharide molecules are generally not affecting the protein by direct interactions. Instead, the QENS and modeling results show that the protein dynamics is slowed down by a slowing down of the protein hydration water, as a result of the “slaving mechanism”. Since the water dynamics and protein motions are slower in the trehalose solution, the results explain the more efficient stabilizing effect of trehalose on proteins. Finally, we will describe a new modelling method, denoted Molecular Dynamics Monte Carlo (MDMC), to model QENS data. The method is under development, and will be a dynamical correspondence to the Empirical Potential Structure Refinement (EPSR) method. 

Register to the seminar by writing an email to contact@snss.se and writing in the subject: Registration to SNSS Webinar Series: Spectroscopy”. Following registration you will be sent a zoom-link to the seminar.