Johnston D.H.,Otterbein College |
Gao L.,University of Oregon |
Lonergan M.C.,University of Oregon
Macromolecules | Year: 2010
The ion density in ionically functionalized polyacetylenes can be controlled by the ring-opening metathesis copolymerization of functionalized cyclooctatetraene (RCOT) monomers. Studies are reported on the kinetics for copolymerization of anionic (M A, R = -CH 2CH 2SO 3 -NMe 4 +) and cationic (M c, R = -CH 2CH 2-NMe 3 +CF 3SO 3 -) RCOTs with a nonionizable RCOT (M T, R = -SiMe 3) initiated by the well-defined tungsten imidoalkylidene catalyst W[CH(o-C 6H 4OMe)](NC 6H 5)[OCCH 3(CF 3) 2] 2(THF). Twenty separate copolymerizations were studied as a function of the mole fraction of ionic monomer in the feedstock. The monomer consumption was observed to follow zero-order behavior over a range of monomer concentration in the M A-M T system, whereas it was observed to follow first-order behavior in the M c-M T system. The zero-order behavior in the M A-M T system was observed to lead to much less drift in polymer composition than predicted by classic copolymerization theory. The initial rates of monomer conversion were determined and used to calculate the copolymer composition curve. The curves exhibited sigmoidal shapes as described by reactivity ratios rc = 8 ± 3 and r T = 4 ± 2 for the M C-M T system and r A = 2.0 ± 0.3 and r T = 2.3 ± 0.3 for the M A-M T system. In all cases, the rate of initiation was observed to be slow relative to propagation, and the initiation rate for MT was observed to be approximately a factor of 4 greater than for the ionic monomers under similar conditions of monomer and catalyst concentration. The observed trends are explained in terms of ion-ion interactions. These interactions are argued to create different local activities of the ionic monomers in the vicinity of an active catalyst center with ultimate ionic monomer as compared to near either the uninitiated catalyst or an active catalyst center with ultimate nonionic monomer. The largest effects are observed in the M C-M T system where, in addition to the largest reactivity ratios, the ratio of the overall polymerization rate to the initiation rate increases by a factor of 20 in progressing from the homopolymerization of M T to that of M c. © 2010 American Chemical Society. Source
Lutterman D.A.,Ohio State University |
Lazinski-Melanson L.A.,Ohio State University |
Asher Y.,Ohio State University |
Johnston D.H.,Otterbein College |
And 2 more authors.
Journal of Photochemistry and Photobiology A: Chemistry | Year: 2011
Two new Ru(II) complexes, [Ru(bpy)2(1-COO-iqu)]+ (2; bpy = 2,2′-bipyridine, 1-COO-iqu- = isoquinoline-1-carboxylate) and [Ru(bpy)2(3-COO-iqu)]+ (3; 3-COO-iqu- = isoquinoline-3-carboxylate), were prepared and their crystal structures solved. The ground and excited state properties of 2 and 3 were characterized and compared to those of [Ru(bpy)3]2+ (1). The presence of the oxygen atom in the Ru(II) coordination sphere makes 2 and 3 easier to oxidize than 1. The Ru → bpy MLCT absorption and emission of 2 and 3 are red-shifted relative to that of 1 in CH2Cl2, and the E00 energies were estimated to be 1.89 eV and 1.95 eV from the low temperature emission of 2 and 3, resulting in excited state oxidation potentials of -1.03 V and -1.10 V vs SCE, respectively. In addition to the short-lived emissive 3MLCT state, a long-lived species is observed in the transient absorption of 3 in DMSO (τ = 49 μs) and pyridine (τ = 44 μs), assigned to a solvent-coordinated complex. This intermediate is not observed for 3 in non-polar solvents or for 2. The absence of the solvent coordinated intermediate in 2 is explained by the stronger Ru-O bond afforded by the lower conjugation in that extends onto the carboxylic acid in the 1-COO-iquo-ligand, compared to that in the 3-COO-iqu -ligand in 3. Transient absorption experiments also show that the 3MLCT excited state of 3 is able to reduce methyl viologen. © 2010 Elsevier B.V. Source
Agency: NSF | Branch: Continuing grant | Program: | Phase: AMO Experiment/Atomic, Molecul | Award Amount: 144.68K | Year: 2016
The goal of this project is to study the Rydberg excitation blockade. Atoms will be cooled to extremely low temperatures and put into high energy states called Rydberg states. In Rydberg states the outermost electron (or the negatively charged component of an atom) travels in extremely large orbits around the nucleus (or the core of an atom). Because of these large orbits, atoms in Rydberg states have properties which are exaggerated relative to the properties of atoms in their natural, or ground state. One such property is that Rydberg atoms interact strongly with each other when separated by large distances, even though they have no net charge. Normally, when a laser is shined on a group of atoms, the outermost electron in each atom is readily promoted to Rydberg states. However, the interactions among multiple Rydberg atoms causes this excitation to be suppressed, or blocked, and leads to the creation of fewer Rydberg atoms than would otherwise be created. This suppression of excitation may help enable the use of single atoms as the bits in computer (neutral atom quantum computing). Quantum computers have the potential to revolutionize data security and encryption. The present project will focus on processes which make the Rydberg excitation blockade function less effectively (state-mixing interactions). Essentially, if one tries to put atoms into a given Rydberg state using a laser, the atoms will mix into other states. This mixing breaks the blockade and leads to an undesirably large number of Rydberg atoms. The goals of the present research are to quantify the extent to which state mixing interactions reduce the blockade efficiency, to understand the physical mechanism which gives rise to the mixing, and to study the experimental parameters which lead to the best excitation blockade. Understanding these issues will allow other researchers to use the blockade in a way that minimizes unwanted effects when developing a quantum computer. The project also involves a significant educational component. The PI will develop educational modules for a diverse group, ranging from general education students to advanced physics students. The PI will also study the impact of metacognitive exercises on problem solving performance in the introductory physics classroom. All work will be done at a primarily undergraduate university with a significant fraction of first-generation college students.
The Rydberg excitation blockade, a process whereby strong interactions among highly-excited atoms suppress laser excitation, has been at the heart of an array of recent experimental achievements. It has been suggested that state-mixing interactions, which result from couplings among multi-particle Rydberg states near a Förster resonance, may compromise the effectiveness of the excitation suppression under otherwise favorable conditions. Experimentally, however, the extent to which the blockade is compromised has been unknown, as large amounts of state mixing have always accompanied an improved blockade near resonance. In this project, the extent to which state-mixing reduces the blockade efficiency will be quantified using state-selective field ionization spectroscopy of rubidium Rydberg atoms in a magneto-optical trap. This work will lead to a better understanding of the physical mechanism responsible for enhanced state-mixing. Additionally, the project will include a systematic study of the experimental conditions for the best blockade near a Förster resonance. The PI will design an eduational module on laser cooling and trapping for a general education course as well as an advanced laboratory experiment on characterizing an ultracold atom cloud in a magneto optical trap.
Agency: NSF | Branch: Continuing grant | Program: | Phase: ELEMENTARY PARTICLE ACCEL USER | Award Amount: 137.01K | Year: 2013
The Otterbein University group of Nathaniel Tagg and his team of undergraduate students will conduct research on neutrino oscillations and interactions using experiments in the Fermilab NuMI and Booster neutrino beams. The research program includes the study of neutrino oscillations (in the MINOS+ experiment), measuring neutrino nucleus cross sections (in the MINERvA experiment), measuring neutrino velocity (MINOS+), and searching for anomalous events that might indicate physics beyond the Standard Model (the MicroBooNE experiment). A special contribution of the group and an exciting broader impact of their research program is the development and implementation of 3D visualization tools to guide the physics analyses of the experiments and to render visible to students and the public the nature of neutrino interactions as recorded and studied by the scientists.
Agency: NSF | Branch: Continuing grant | Program: | Phase: ADVANCE - IT-START | Award Amount: 159.80K | Year: 2012
The PIs at Otterbein College will conduct a self assessment in the areas of bias/climate, service obligations, work-life balance, and issues surrounding invisible women (e.g., adjunct, part-time, those not well integrated into departments.) They will use existing data sources as well as subscribe to the COACHE survey. They will interview women who have left Otterbein, and convene focus groups of invisible women. They plan to institutionalize some data collection efforts. In addition they will utilize the existing mechanism of Professional Learning Communities to bring ADVANCE topics to the faculty. Otterbein is a PUI and aligns their activities well with the specific needs of PUIs. In particular the focus on ?invisible women? is very relevant as many institutions are increasing their non-tenure-track faculty, especially PUIs. Results could prove to have national significance.