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Although the dynamics of collisions between a molecule and a solid surface are ultimately quantum mechanical, decohering effects owing to the large number of interacting degrees of freedom typically obscure the wavelike nature of these events. However, a partial decoupling of internal molecular motion from external degrees of freedom can reveal striking interference effects despite significant momentum exchange between the molecule and the bath of surface vibrations. We report state-prepared and state-resolved measurements of methane scattering from a room-temperature gold surface that demonstrate total destructive interference between molecular states related by a reflection symmetry operation. High-contrast interference effects prevail for all processes investigated, including vibrationally excited and vibrationally inelastic collisions. The results demonstrate the distinctly quantum mechanical effect of discrete symmetries in molecular collision dynamics. 

Atomic-scale structures that account for the acceleration of reactivity by heterogeneous catalysts often form only under reaction conditions of high temperatures and pressures, making them impossible to observe with low-temperature, ultra-high-vacuum methods. We present velocity-resolved kinetics measurements for catalytic hydrogen oxidation on palladium over a wide range of surface concentrations and at high temperatures. The rates exhibit a complex dependence on oxygen coverage and step density, which can be quantitatively explained by a density functional and transition-state theory–based kinetic model involving a cooperatively stabilized configuration of at least three oxygen atoms at steps. Here, two oxygen atoms recruit a third oxygen atom to a nearby binding site to produce an active configuration that is far more reactive than isolated oxygen atoms. Thus, hydrogen oxidation on palladium provides a clear example of how reactivity can be enhanced on a working catalyst. 

Surface reaction rate constants were measured accurately so that a meaningful comparison with theory can now be made. 

Despite the critical role of teachers in the educational process, few advanced learning technologies have been developed to support teacher-instruction or professional development. This lack of support is particularly acute for middle school math teachers, where only 37% felt well prepared to scaffold instruction to address the needs of diverse students in a national sample. To address this gap, the Advancing Middle School Teachers’ Understanding of Proportional Reasoning project is researching techniques to apply pedagogical virtual agents and dialog-based tutoring to enhance teachers' content knowledge and pedagogical content knowledge. This paper describes the design of a conversational, agent-based intelligent tutoring system to support teachers' professional development. Pedagogical strategies are presented that leverage a virtual human facilitator to tutor pedagogical content knowledge (how to teach proportions to students), as opposed to content knowledge (understanding proportions). The roles for different virtual facilitator capabilities are presented, including embedding actions into virtual agent dialog, open-response versus choice-based tutoring, ungraded pop-up sub-activities (e.g. whiteboard, calculator, note-taking). Usability feedback for a small cohort of instructors pursuing graduate studies was collected. In this feedback, teachers rated the system ease of use and perceived usefulness moderately well, but also reported confusion about what to expect from the system in terms of flow between lessons and support by the facilitator. 

Adsorption involves molecules colliding at the surface of a solid and losing their incidence energy by traversing a dynamical pathway to equilibrium. The interactions responsible for energy loss generally include both chemical bond formation (chemisorption) and nonbonding interactions (physisorption). In this work, we present experiments that revealed a quantitative energy landscape and the microscopic pathways underlying a molecule’s equilibration with a surface in a prototypical system: CO adsorption on Au(111). Although the minimum energy state was physisorbed, initial capture of the gas-phase molecule, dosed with an energetic molecular beam, was into a metastable chemisorption state. Subsequent thermal decay of the chemisorbed state led molecules to the physisorption minimum. We found, through detailed balance, that thermal adsorption into both binding states was important at all temperatures.