This work will obtain precise measurements of the fine structure of high-angular momentum Rydberg states of rotationally excited molecular hydrogen, H2. This study will lead to precise determinations of such fundamental properties of the molecular hydrogen ion as multipole moments, polarizabilities and hyperfine constants. Of particular interest are the properties of the rotationally excited states (R=2 and 3) of the ground vibrational state (v=0) of H2+ that have thus far been experimentally inaccessible. There are few existing direct measurements of H2+ because of the lack of stable excited states. However, an excited electron, bound to an ion core, in a large nearly circular orbit can act as a very sensitive probe to investigate electric and magnetic properties of the ion core. High angular momentum Rydberg states meet this criterion and, therefore, precise studies of these spectra afford the opportunity to detect long-range properties of the ion. The basic model in molecular physics, H2+, has been studied extensively by theorists, but there are comparatively few precise experimental measurements. The need for accurate models beyond the adiabatic approximation is increasing, and several theoretical approaches have been developed. This study will provide an excellent avenue to test the accuracy of the theoretical models. A novel approach to the detection techniques of Resonant Excitation Stark Ionization Spectroscopy (RESIS) will allow the first measurements of the higher rotational levels of H2 that were unattainable in previous studies due to their fast autoionization rates. This work will provide precise measurements relevant to the advances in H2+ theory, which are necessary in other areas such as ultracold molecules and interstellar chemistry. The new measurements will also provide immediate improvement to the best existing spectral measurement in H2+.
The experimental program will have broad impact at three levels. First, undergraduate students at State University of New York at Fredonia in general would be positively impacted though the modeling of an active researcher, infusion of current research into course work, active participation in research, and experience in presenting research results at multiple levels. Studies in the precise measurement of the fine structure of high-L Rydberg states offers students the opportunity to gain experience with several types of equipment used quite universally in research labs. In addition, the theoretical analysis of these nearly classical high-L Rydberg systems can be understood by an upper-level undergraduate student. It clearly demonstrates the use of perturbation theory in quantum mechanics, and several concepts a student would learn in a typical electricity and magnetism course, such as the multipole expansion. This research project will be used for discussion of various topics in the PI's undergraduate classroom, in a range of courses from algebra-based physics to 400-level physics courses. Second, the funding of this research program will help establish the career of a new faculty researcher, increase the on-campus experimental research, develop interdisciplinary research interests between the Departments of Physics and Chemistry, and further expand the presence of atomic, molecular, and optical physics at small undergraduate institutions. Third, the research at a rurally situated public university of higher education, which is part of the K-16 educational pipeline, positively impacts undergraduate students who are underrepresented in the STEM pipeline such as women, economically disadvantaged students who enter higher education through community college and continue through publicly funded regional universities, first generation college students, and students who come from rural, geographically isolated areas. Presentations at local community colleges and/or other regional institutions in this rural area positively extend the impact of this research into this under-served area.
