Guided ion beam kinetic energy thresholds in the ion–molecule reactions M++H2→MH++H, where M+=B+, Al+, and Ga+ exceed by 0.4–∼5 eV the thermodynamic energy requirements or theoretically computed barrier heights of these reactions. In addition, the formation of MD+ occurs at a significantly lower threshold than MH+ when M+ reacts with HD. Moreover, the measured reaction cross sections for production of MH+ product ions are very small (10−17–10−20 cm2). These facts suggest that a ‘‘dynamical bottleneck’’ may be operative in these reactions. In this work, the eigenvalues of the mass-weighted Hessian matrix, which provide local normal-mode frequencies, are used to identify locations on the ground-state MH2+ potential energy surfaces where collisional-to-internal energy transfer can readily take place. In particular, the potential energies at geometries where eigenvalues corresponding to interfragment and to internal motions undergo avoided crossings are related to the kinetic energies of apparent reaction thresholds. This near-resonance energy transfer model, applied to M++HD reactions, displays the experimentally observed preference to form MD+ at lower collision energies than MH+ as well as the fact that reaction thresholds may greatly exceed thermodynamic energy requirements. This model explains the small reaction cross sections in terms of high energy content and subsequent dissociation of nascent MH+ (or MD+) ions. Although the mass-weighted Hessian matrix is used as a tool in this analysis, the model put forth here is not equivalent to a reaction-path Hamiltonian dynamics approach.

Proton-transfer reactions involving the silaformyl anion, HSiO-, and its conjugate acids, HSiOH and H2SiO, have been investigated with ab initio methods. Calculations through fourth-order perturbation theory suggest possible routes for proton transfer. Accurate estimates for the acidity of H2SiO and HSiOH are presented and discussed in light of earlier experimental estimates. Disciplines Chemistry CommentsReprinted (adapted) Abstract: Proton-transfer reactions involving the silaformyl anion, HSiO -, and its conjugate acids, HSiOH and H 2 SiO, have been investigated with ab initio methods. Calculations through fourth-order perturbation theory suggest possible routes for proton transfer. Accurate estimates for the acidity of H 2 SiO and HSiOH are presented and discussed in light of earlier experimental estimates.

Two days after the University of Utah Seismograph Stations (UUSS) staff were required to leave campus and work remotely, an Mw 5.7 earthquake struck the Salt Lake Valley near the town of Magna, Utah. This event was the largest instrumentally recorded earthquake in the Salt Lake Valley and the largest earthquake ever felt by most residents. The timing of this event—at the start of a lockdown in response to the COVID-19 pandemic—made the UUSS response to this earthquake an extra challenge. Other factors such as a toxic plume caused by the ground shaking, inclement weather, and a mountain lion also impacted the work. The response tested the continuity of operations plan that had been in place since 2007, response protocols, and communications with partners and the public. Overall, the UUSS earthquake response was successful: A valuable and arguably unprecedented dataset of strong ground motions from normal faulting was generated, magnitudes and locations of thousands of earthquakes were shared in a timely fashion, unfounded rumors and general questions were promptly responded to via traditional and social media, and initial scientific results were submitted for publication.

The interaction of Al' (IS) ions with HZ on the lowest electronic energy surface is studied using ab initio electronic structure methods. A Cs symmetry transition state is located and found to have the geometry of a product AlH+ ion loosely bound to a H atom, consistent with the Hammond postulate for this endothermic reaction. Locating this transition state, beginning at geometries that characterize vibrationally cold H2 and translationally hot AI' , posed special challenges to the commonly used "hill-climbing'' algorithm because of regions of geometrical instability along the path thus generated. This instability was found to be a result of second-order Jahn-Teller coupling with a low-lying ' B 2 electronic state. In addition to these primary findings, a weakly bound T-shaped AI+---H2 Cz, van der Waals complex is found that lies only 242 cm-' below the AI' and HZ asymptote, with H-H internuclear separation only slightly distorted from the equilibrium bond distance of HZ and an AI-H distance (3.5 A) much longer than the covalent bond length in AIH+ (1.6 A). The locally stable but thermodynamically unstable linear HAIH+ ('2;) species and, of course, the H + AIH+(*L+) reaction products have also been identified as critical points on the ground-state surface. Where known, the geometries and energies that we calculate agree well with experimental data.

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