A novel merged beam apparatus to study the cosmic origins of organic chemistry

Reactions of atomic carbon with molecular ions play a critical role for gas phase molecular formation in interstellar clouds. These interactions are the first links in the chain of chemical reactions leading to the synthesis of complex organic species. Much of our knowledge of this process is through spectroscopic observations and theoretical models. However, our understanding of this chemistry is constrained by uncertainties in the underlying reaction rate coefficients. Data from quantum calculations are limited to reactions involving three or fewer atoms. Meanwhile, previous experimental studies have been hampered by the difficulty in generating a sufficiently intense and well characterized neutral carbon beam. To address these issues and to study these reactions experimentally, we are building a novel laboratory device which does not suffer from such limitation

A simple double-focusing electrostatic ion beam deflector

We have developed an electrostatic, double-focusing 90° deflector for fast ion beams consisting of concentric cylindrical plates of differing heights. In contrast to standard cylindrical deflectors, our design allows for focusing of an incoming parallel beam not only in the plane of deflection but also in the orthogonal direction. The optical properties of our design resemble those of a spherical capacitor deflector while it is much easier and more cost effective to manufacture

Recommended Thermal Rate Coefficients for the C + H3+ Reaction and Some Astrochemical Implications

We incorporate our experimentally derived thermal rate coefficients for C + ${{\rm{H}}}_{3}^{+}$ forming CH+ and CH2 + into a commonly used astrochemical model. We find that the Arrhenius–Kooij equation typically used in chemical models does not accurately fit our data and instead we use a more versatile fitting formula. At a temperature of 10 K and a density of 104 cm−3, we find no significant differences in the predicted chemical abundances, but at higher temperatures of 50, 100, and 300 K we find up to factor of 2 changes. In addition, we find that the relatively small error on our thermal rate coefficients, ~15%, significantly reduces the uncertainties on the predicted abundances compared to those obtained using the currently implemented Langevin rate coefficient with its estimated factor of 2 uncertainty

Recommended Thermal Rate Coefficients for the C + H3+ Reaction and Some Astrochemical Implications

We incorporate our experimentally derived thermal rate coefficients for C + ${{\rm{H}}}_{3}^{+}$ forming CH+ and CH2 + into a commonly used astrochemical model. We find that the Arrhenius–Kooij equation typically used in chemical models does not accurately fit our data and instead we use a more versatile fitting formula. At a temperature of 10 K and a density of 104 cm−3, we find no significant differences in the predicted chemical abundances, but at higher temperatures of 50, 100, and 300 K we find up to factor of 2 changes. In addition, we find that the relatively small error on our thermal rate coefficients, ~15%, significantly reduces the uncertainties on the predicted abundances compared to those obtained using the currently implemented Langevin rate coefficient with its estimated factor of 2 uncertainty

Alternate Fuel Cell Membranes for Energy Independence

The overall objective of this project was the development and evaluation of novel hydrocarbon fuel cell (FC) membranes that possess high temperature performance and long term chemical/mechanical durability in proton exchange membrane (PEM) fuel cells (FC). The major research theme was synthesis of aromatic hydrocarbon polymers of the poly(arylene ether sulfone) (PAES) type containing sulfonic acid groups tethered to the backbone via perfluorinated alkylene linkages and in some cases also directly attached to the phenylene groups along the backbone. Other research themes were the use of nitrogen-based heterocyclics instead of acid groups for proton conduction, which provides high temperature, low relative humidity membranes with high mechanical/thermal/chemical stability and pendant moieties that exhibit high proton conductivities in the absence of water, and synthesis of block copolymers consisting of a proton conducting block coupled to poly(perfluorinated propylene oxide) (PFPO) blocks. Accomplishments of the project were as follows: 1) establishment of a vertically integrated program of synthesis, characterization, and evaluation of FC membranes, 2) establishment of benchmark membrane performance data based on Nafion for comparison to experimental membrane performance, 3) development of a new perfluoroalkyl sulfonate monomer, N,N-diisopropylethylammonium 2,2-bis(p-hydroxyphenyl) pentafluoropropanesulfonate (HPPS), 4) synthesis of random and block copolymer membranes from HPPS, 5) synthesis of block copolymer membranes containing high-acid-concentration hydrophilic blocks consisting of HPPS and 3,3'-disulfonate-4,4'-dichlorodiphenylsulfone (sDCDPS), 6) development of synthetic routes to aromatic polymer backbones containing pendent 1H-1,2,3-triazole moieties, 7) development of coupling strategies to create phase-separated block copolymers between hydrophilic sulfonated prepolymers and commodity polymers such as PFPO, 8) establishment of basic performance properties of experimental membranes, 9) fabrication and FC performance testing of membrane electrode assemblies (MEA) from experimental membranes, and 10) measurement of ex situ and in situ membrane durability of experimental membranes. Although none of the experimental hydrocarbon membranes that issued from the project displayed proton conductivities that met DOE requirements, the project contributed to our basic understanding of membrane structure-property relationships in a number of key respects. An important finding of the benchmark studies is that physical degradation associated with humidity and temperature variations in the FC tend to open new fuel crossover pathways and act synergistically with chemical degradation to accelerate overall membrane degradation. Thus, for long term membrane survival and efficient fuel utilization, membranes must withstand internal stresses due to humidity and temperature changes. In this respect, rigid aromatic hydrocarbon fuel cell membranes, e.g. PAES, offer an advantage over un-modified Nafion membranes. The benchmark studies also showed that broadband dielectric spectroscopy is a potentially powerful tool in assessing shifts in the fundamental macromolecular dynamics caused by Nafion chemical degradation, and thus, this technique is of relevance in interrogating proton exchange membrane durability in fuel cells and macromolecular dynamics as coupled to proton migration, which is of fundamental relevance in proton exchange membranes in fuel cells. A key finding from the hydrocarbon membrane synthesis effort was that rigid aromatic polymers containing isolated ion exchange groups tethered tightly to the backbone (short tether), such as HPPS, provide excellent mechanical and durability properties but do not provide sufficient conductivity, in either random or block configuration, when used as the sole ion exchange monomer. However, we continue to hypothesize that longer tethers, and tethered groups spaced more closely within the hydrophilic chain elements of the polymer, will yield highly conductive materials with excellent mechanical properties. Another key finding is the superior performance of PAES membranes upon being subjected to open circuit voltage (OCV) testing. Throughout the course of the experiment, OCV for the PAES not only stayed higher but also decayed at a much lower rate, which is attributed to better dimensional stability and improved mechanical and gas barrier properties. The rigid backbone reinforcement of PAES adds gas diffusion tortuosity that restricts membrane degradation and OCV loss due to reduced fuel crossover. The overall results of creep, contractile stress and mechanical tensile tests confirm the conclusion that degraded MEAs of PAES membrane can handle stress and are more likely to be more durable in a fuel cell, even after subjected to 62h of OCV degradation

Reaction Studies of Neutral Atomic C with H3+ using a Merged-beams Apparatus

We have investigated the chemistry of C + H_3^+ forming CH+, CH_2^+, and CH_3^+. These reactions are believed to be some of the key gas-phase astrochemical processes initiating the formation of organic molecules in molecular clouds. For this work, we have constructed a novel merged fast-beams apparatus which overlaps a beam of molecular ions onto a beam of ground-term neutral atoms. Here, we describe the apparatus in detail and present cross section data for forming CH+ and CH_2^+ at relative energies from ≈9 meV to ≈20 and 3 eV, respectively. Measurements were performed for statistically populated C (3P_J) in the ground term reacting with hot H_3^+ (at an internal temperature of ~2550 K). Using these data, we have derived rate coefficients for translational temperatures from ≈72 K to ~2.3 X 10^5 and 3.4 X 10^4 K, respectively. For the formation of CH_3^+, we are only able to place an upper limit on the rate coefficient. Our results for CH+ and CH_2^+ are in good agreement with the mass-scaled results from a previous ion trap study of C + D_3^+, at a translational temperature of ~1000 K. That work also used statistically populated C (3P_J) but internally cold D_3^+ (~77 K). The good agreement between the two experiments implies that the internal excitation of the H_3^+ is not significant so long as the reaction proceeds adiabatically. At 300 K, the C fine-structure levels are predicted to be essentially statistically populated, enabling us to compare our translational temperature results to thermal equilibrium calculations. At this temperature, our rate coefficient for forming CH+ lies a factor of ≈2.9 below the Langevin rate coefficient currently given in astrochemical databases, and a factor of ~1.8-3.3 below the published classical trajectory studies using quantum mechanical potential energy surfaces. Our results for CH_2^+ formation at 300 K are a factor of ≈26.7 above these semi-classical results. Astrochemical databases do not currently include this channel. We also present a method for converting our translational temperature results to thermal rate coefficients for temperatures below ~300 K. The results indicated that CH_2^+ formation dominates over that of CH+ at temperatures ~<50 K

Improved functionalization of oleic acid-coated iron oxide nanoparticles for biomedical applications

Superparamagnetic iron oxide nanoparticles can providemultiple benefits for biomedical applications in aqueous environments such asmagnetic separation or magnetic resonance imaging. To increase the colloidal stability and allow subsequent reactions, the introduction of hydrophilic functional groups onto the particles’ surface is essential. During this process, the original coating is exchanged by preferably covalently bonded ligands such as trialkoxysilanes. The duration of the silane exchange reaction, which commonly takes more than 24 h, is an important drawback for this approach. In this paper, we present a novel method, which introduces ultrasonication as an energy source to dramatically accelerate this process, resulting in high-quality waterdispersible nanoparticles around 10 nmin size. To prove the generic character, different functional groups were introduced on the surface including polyethylene glycol chains, carboxylic acid, amine, and thiol groups. Their colloidal stability in various aqueous buffer solutions as well as human plasma and serum was investigated to allow implementation in biomedical and sensing applications.status: publishe

Neuromatch Academy: a 3-week, online summer school in computational neuroscience

Neuromatch Academy (https://academy.neuromatch.io; (van Viegen et al., 2021)) was designed as an online summer school to cover the basics of computational neuroscience in three weeks. The materials cover dominant and emerging computational neuroscience tools, how they complement one another, and specifically focus on how they can help us to better understand how the brain functions. An original component of the materials is its focus on modeling choices, i.e. how do we choose the right approach, how do we build models, and how can we evaluate models to determine if they provide real (meaningful) insight. This meta-modeling component of the instructional materials asks what questions can be answered by different techniques, and how to apply them meaningfully to get insight about brain function