Step-by-step state-selective tracking of fragmentation dynamics of water dications by momentum imaging.

The double photoionization of a molecule by one photon ejects two electrons and typically creates an unstable dication. Observing the subsequent fragmentation products in coincidence can reveal a surprisingly detailed picture of the dynamics. Determining the time evolution and quantum mechanical states involved leads to deeper understanding of molecular dynamics. Here in a combined experimental and theoretical study, we unambiguously separate the sequential breakup via D+ + OD+ intermediates, from other processes leading to the same D+ + D+ + O final products of double ionization of water by a single photon. Moreover, we experimentally identify, separate, and follow step by step, two pathways involving the b 1Σ+ and a 1Δ electronic states of the intermediate OD+ ion. Our classical trajectory calculations on the relevant potential energy surfaces reproduce well the measured data and, combined with the experiment, enable the determination of the internal energy and angular momentum distribution of the OD+ intermediate.

Getting Everyone to the Fair: Supporting Teachers in Broadening Participation in Science and Engineering Fairs.

Science and Engineering (S&E) fairs are a valuable educational activity and are believed to increase students' engagement and learning in science and engineering. However, due to differences in resources, many schools do not implement fairs to achieve these benefits for their students. This study reports the findings of a program intended to increase the participation of students from low-achieving and under-resourced schools in a regional fair program that feeds into the international fair competition. We found that the number of schools and projects participating in our regional fair increased dramatically since the start of the program. Teachers had mostly positive expectations for the project and expressed buy-in for the effort the project would take. They recruited a diverse pool of students to participate in the school fairs. Quasi-experimental methods allowed us to explore the impact of completing S&E fairs on student gains on science self-efficacy, interest and value perceptions. Controlling for pre-existing differences in these attitudes, we found that students not completing projects showed declines in their science attitudes during the year. Students who completed projects maintained similar attitudes, while those whose projects advanced to the regional fair had substantial gains on all three variables. It is unknown whether this gain can be attributed to the experience of engaging with a quality project, from being the kind of student who completes a quality project, or some other factor. Future research with greater experimental control could address these questions.