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Electron-ion coincidence measurements of molecular dynamics with intense X-ray pulses
Get PDFMolecules can sequentially absorb multiple photons when irradiated by an intense X-ray pulse from a free-electron laser. If the time delay between two photoabsorption events can be determined, this enables pump-probe experiments with a single X-ray pulse, where the absorption of the first photon induces electronic and nuclear dynamics that are probed by the absorption of the second photon. Here we show a realization of such a single-pulse X-ray pump-probe scheme on Nmolecules, using the X-ray induced dissociation process as an internal clock that is read out via coincident detection of photoelectrons and fragment ions. By coincidence analysis of the kinetic energies of the ionic fragments and photoelectrons, the transition from a bound molecular dication to two isolated atomic ions is observed through the energy shift of the inner-shell electrons. Via ab-initio simulations, we are able to map characteristic features in the kinetic energy release and photoelectron spectrum to specific delay times between photoabsorptions. In contrast to previous studies where nuclear motions were typically revealed by measuring ion kinetics, our work shows that inner-shell photoelectron energies can also be sensitive probes of nuclear dynamics, which adds one more dimension to the study of light-matter interactions with X-ray pulses
Real-time observation of ultrafast molecular rotation in weakly bound dimers
Get PDFThe fragmentation dynamics of dicationic dimers of acetylene molecules initiated upon strong-field laser ionization is studied. Time-resolved pump-probe experiments with femtosecond laser pulses, accompanied by ab initio dynamical calculations, allow us to evaluate the detailed behavior of molecular ions during the dissociation process. The dynamical properties of the intermediate C2H+2⋯C2H+2 state created by the pump pulse are probed by a second pulse which causes further ionization. The time-dependent yield of a coincident C2H+2 + C2H22+ ion pair exhibits an oscillation feature with a periodicity of 240 ± 30 fs. Our studies demonstrate that this is caused by an ultrafast rotation of C2H+2 cations driven by intermolecular Coulomb force together with the orientation-dependent ionization rate. We suggest that the present observation of ultrafast molecular rotation can be a general phenomenon occurring in a wide variety of systems
The COLTRIMS Reaction Microscope—The Spyhole into the Ultrafast Entangled Dynamics of Atomic and Molecular Systems
No full textThe COLTRIMS Reaction Microscope C-REMI can image the momentum vectors of all emitted charged fragments in an atomic or molecular reactions similar to the bubble chamber in high energy particle physics. C-REMI can detect fragments with “zero” kinetic energy in an ultrahigh vacuum environment by projecting them with weak electromagnetic fields onto position-sensitive detectors. Geometrically a nearly 4π collection solid angle and a nearly 50% efficiency for a fivefold multi-coincidence can be achieved. Measuring time-of-flight and detector position the momenta of the fragments can be measured with excellent resolution (<0.01 a.u.; see A1 in the Appendix). Thus, multivector correlations in momentum space are measured, which provide insight into the entangled dynamics of atomic and molecular quantum systems. From these vector-correlations phases and energies can be deduced which allow for relative time measurements even in the zeptosecond range. C-REMI provides a “spyhole” into the secrets of ultrafast dynamics of atomic and molecular processes. It is applied today around the globe in numerous research projects in physics and chemistry. The purpose for writing this article is to demonstrate the universal application possibilities of C-REMI, and its high multi-coincidence efficiency and high momentum resolution. This paper will not give a review on all milestone experiments performed with C-REMI
Extended quantitative rescattering model for simulating high-order harmonic streaking spectra by synchronization of an intense IR laser and a time-delayed attosecond XUV pulse
Get PDFWe theoretically investigate the modulated high-harmonic generation (HHG) driven by an intense few-cycle infrared (IR) laser field and a weak extreme-ultraviolet (XUV) pulse at a delayed time. We establish an extended quantitative rescattering (EQRS) model to simulate the HHG streaking spectra, with the ideas of correcting the IR ionization and the transition from the ground to continuum states in the strong-field approximation. The EQRS model has an accuracy comparable to that from “exactly” solving the time-dependent Schrödinger equation (TDSE). We reveal that the fringes in the streaking spectra are caused by the interference between the attosecond XUV pulse and harmonics resulting from different recombination pathways under the intense IR laser. We then demonstrate that the XUV pulse can be accurately retrieved by treating the single-atom TDSE results or macroscopic propagation results as the “input” data. This work provides with a tool for efficiently simulating and thoroughly analyzing the XUV-assisted HHG, which could also enhance its capability for tracing the electron dynamics involved in the strong-field phenomena
Fragmentation of CF4q+ (q=2,3) induced by 1-keV electron collisions
Get PDFWe report on an investigation on the fragmentation dynamics of CF4q+ (q=2,3) induced by 1-keV electron collisions utilizing an ion momentum imaging spectrometer. From the time-of-flight correlation maps five dominating dissociation channels of CF42+ as well as one three-body fragmentation channel of CF43+ are identified. The kinetic energy release (KER) distributions for these channels are obtained and compared with the data available in the literature. The Dalitz-like momentum diagram and the Newton diagram are employed to analyze the breakup mechanism in the three-body fragmentation channel. We found that, for CF42+ dissociation into F++CF2++F, F++CF++2F, and F++F++CF2, the concerted breakup is the dominating process. Channel C++F++3F is dominated by the initial charge separation, i.e., CF42+→F++CF++2F→C++F++3F. With the help of the native frame method, we assigned one sequential pathway and two concerted pathways for channel CF43+→F++F++CF2+. The branching ratios of these pathways are determined. The momentum correlation of the fragments and the deduced KER distribution indicate that different excited states of CF43+ with different geometries are responsible for these three pathways. The Coulomb explosion model simulation shows that most of the events in this channel are produced by CF43+ ions that have deformed geometries from the neutral CF4 molecule
Effect of Concrete Properties and Prestressing Steel Reinforcement Type on the Development Length in Pretensioned Concrete Railroad ties
Get PDFA study was conducted to determine the effect of different concrete properties and prestressing steel reinforcement type on the development length and flexural capacity of prestressed concrete railroad ties. Thirteen different 5.32-mm-diameter prestressing wires and six different strands (four 7-wire strands and two 3-wire strands) were used to fabricate 4-tendon pretensioned prisms with a square cross section. A consistent concrete mixture utilizing Type III cement and a water-to-cementitious ratio of 0.32 was used for all prisms. The prisms were detensioned at concrete compressive strengths of 3500 psi, 4500 psi, and 6000 psi. Load tests revealed that there is a large difference in the development length for different wire/strand types as well as with different concrete release strengths. Additionally, cyclic load tests revealed that there is also a significant difference in the bond performance of these reinforcement types under repeated loadings
Use of 3D Non-Contact Profilometry to Quantify Indent Characteristics of Prestressing Wires Used in Pretensioned Concrete Railroad Ties
Get PDFThe objective of this research was to investigate possible correlation between prestressing wire indent geometry and the performance of pretensioned concrete members fabricated with these same reinforcements. Thirteen (13) commercially available and twelve (12) custom-made reinforcement wires were evaluated. A new non-contact indent profiling system was developed to collect detailed surface profiles of the prestressing steel. New geometrical feature measurements and processing algorithms were developed to provide detailed measurement of prestressing steel according to the dimensioning and tolerancing guidelines of ASME Y14.5-2009. These geometrical features were found to have significant correlation with the transfer length and fracture propensity of concrete crossties. Models were created to predict the transfer length of concrete crossties based on the extracted indent characteristics
Trigger Warning: What to do with the ugly history that lurks in your archives
Get PDFSo you’ve encountered materials in your institutional collection showcasing histories of racism, sexism, and other forms of bigotry. You’ve gone through the process of appraising these materials, describing them, and making them accessible to the public. You’ve even added a content warning to your collections to let researchers know they may encounter offensive materials. What now? In this audio piece, three information professionals from Kansas State University will tackle the “what’s next” of working with controversial collection materials. The speakers will then guide listeners through some of the legal and ethical requirements for archivists seeking to highlight these materials and we will discuss how to use these materials to create learning opportunities for our students, faculty, and staff
Effects of a Range of Amphetamine Exposure Doses on Devaluation Testing with Mismatched Training-Test Cues in Male Rats
Get PDFCharles PickensPast evidence shows that drug use may impair decision-making ability. The specific nature of this relationship and direction of its causality are unclear, however, there is evidence to support that chronic amphetamine (amp) use could affect decision-making processes. Animal models are a controlled way to assess issues of this causality. Amp is a dopamine agonist which stimulates the CNS and is a treatment for ADHD. Therefore, chronic administration of amp can model the chronic use of stimulants in humans. This has important implications because one of the most commonly prescribed stimulants, Adderall, is essentially pharmaceutical grade amphetamine. People sometimes take these stimulants for long periods of time which is why we wanted to see if they have long-term effects on decision-making. In order to examine this relationship, rats were tested in a devaluation procedure following the chronic administration of amphetamines. Devaluation tasks are used to model flexible goal-directed decision-making. The devaluation task used in this study involved rats learning to pair two dissociable lever-light compound cues with different food outcomes. One outcome was then devalued using selective satiety, reducing motivation for a specific food reward by unlimited consumption of that particular food. Devaluation is successful if rats no longer respond to obtain the devalued reward after being presented the cue. Our results suggest that chronic administration of amp exposure appears to have lasting impairments on decision making. These impairments were only found during behavioral testing and not training. This suggests that the brain areas involved are likely the orbitofrontal and prelimbic cortex, as they are related to impairments in devaluation effects. This study has implications because it’s results could be related to those who consume ADHD medication on a daily basis. Future research will include the addition of more rats to see if the same effects are found. If so, perfused brains will undergo Fos examination
2020 Virtual K-State First Celebration
No full textIn a virtual celebration, K-State First presents the winners for the 2020 First-Year Student Advocate and K-State First Book awards.
The 2020 First-Year Advocate Award winners:
Faculty/staff recipient - Jessica Henault
Student recipient - Julia Gross
K-State First Book Awards:
Faculty/staff recipient - Suzanne Porath
Student group recipient - Minorities in Agriculture, Natural Resources and Related Sciences or MANRRS
Student recipients - Grace Huynh and Bailey Robert