The stabilty and the molecular properties of thiiranimine are studied by using ab initio MO methods. Geometries are optimized at the HF/631G* and MP2/631G** levels while relative energies are estimated at the MP4/631G** level together with the zero-point energies. Our analysis pointa out that the interaction between the C-N moiety and the three-membered ring is responsible for several unusual properties of thiiranimine such as the high C=N stretching frequency, the relatively small ring strain (as compared with thiirane), and the large proton affinity at nitrogen. Our calculations also suggest that the first photoelectron band is due to an S ionization and that the first UV band arisea ementially from an intraatomic sulfur transition. The fragmentation reaction is endothermic, but consideration of entropy terms modifies the picture significantly. The resulting free energies show that thiiranimine is quite stable towards fragmentation into hydrogen isocyanide plus thioformaldehyde in agreement with experiments on substituted thiiranimines. Finally, the regiochemistry of thiiranimine in cycloadditions is also discussed on the basis of the frontier orbitals.

Chemists are frequently called upon to set up, troubleshoot, and repair-and sometimes construct-the instruments they use for analytical measurements. These challenges may occur in industrial settings or in graduate school. The first experience in "looking under the hood" of an analytical instrument can be quite intimidating. To reduce this fear of the unknown, it seemed reasonable to extend to students an introductory opportunity for hands-on experience with some examples of the essential components of modern instruments (signal transducers, electronic circuits, and computer hardware and software).

"NASA's Advanced Exploration Systems (AES) program is pioneering new approaches for rapidly developing prototype systems, demonstrating key capabilities, and validating operational concepts for future human missions beyond Earth orbit" (NASA 2012). These forays beyond the confines of earth's gravity will place unprecedented demands on launch systems. They must not only blast out of earth's gravity well as during the Apollo moon missions, but also launch the supplies needed to sustain a crew over longer periods for exploration missions beyond earth's moon. Thus all spacecraft systems, including those for the separation of metabolic carbon dioxide and water from a crewed vehicle, must be minimized with respect to mass, power, and volume. Emphasis is also placed on system robustness both to minimize replacement parts and ensure crew safety when a quick return to earth is not possible. Current efforts are focused on improving the current state-of-the-art systems utilizing fixed beds of sorbent pellets by seeking more robust pelletized sorbents, evaluating structured sorbents, and examining alternate bed configurations to improve system efficiency and reliability. These development efforts combine testing of sub-scale systems and multi-physics computer simulations to evaluate candidate approaches, select the best performing options, and optimize the configuration of the selected approach, which is then implemented in a full-scale integrated atmosphere revitalization test. This paper describes the carbon dioxide (CO2) removal hardware design and sorbent screening and characterization effort in support of the Atmosphere Resource Recovery and Environmental Monitoring (ARREM) project within the AES program. A companion paper discusses development of atmosphere revitalization models and simulations for this project.

Carbon‐centered radicals have historically been classified as either persistent or reactive in solution. Little attention has been given to finding a relationship between this reactivity and the steric hindrance of radicals. The bimolecular coupling rate constants of some aryl‐substituted fluorenyl and xanthenyl radicals were determined utilizing fast‐scan cyclic voltammetry and digital simulations. This rate constant was found to be attenuated from the diffusion‐limited value as the twist of the aryl substituent increased; the twist was described by an appropriate dihedral angle (Θ). However, Θ was found to be insufficient to represent the steric shielding provided by the aryl groups. Instead, thickness parameters (Z) obtained from MOPAC RHF‐PM3 calculations correlated well (R2 = 0.954) with the coupling rate constants of the radicals considered. This parameter was taken as the greatest extent of the van der Waals surface in the area of the p‐orbital holding the unpaired electron. Copyright © 2000 John Wiley & Sons, Ltd.