In this project, funded by the Experimental Physical Chemistry Program of the Chemistry Division, Prof. Thomas D. Varberg of Macalester College and his undergraduate research students will record and analyze the electronic spectra of transition metal-containing diatomic molecules such as AuF, TaH, TaF, and TaO. By fitting parameterized molecular Hamiltonians to the measured transitions, the investigators will determine accurate values for the important molecular constants and the bond lengths. The nuclear hyperfine structure of the molecules will be studied at higher resolution by intermodulated fluorescence spectroscopy. The analysis of the hyperfine structure will illuminate details of the bonding in these metal free radicals. Understanding such molecules is important to fields as diverse as astronomy, catalysis, metallurgy and organometallic chemistry. Diatomic molecules containing a transition metal display the simplest form of metal bonding and are therefore relevant as initial models for more complex systems.
Besides the potential broader scientific impact of the proposed research, Prof. Varberg will continue to provide his undergraduate collaborators with valuable research experience, which will help them to pursue careers in science and technology.
The scientific goals and intellectual merits of this project were to obtain and analyze highly accurate spectroscopic information on the structure of transition metal-containing gaseous free radicals. We targeted five different molecules during the course of this project: tantalum oxide (TaO), tantalum sulfide (TaS), tantalum hydride (TaH), gold fluoride (AuF), and gold sulfide (AuS). We investigated the gas-phase electronic spectra of these molecules using laser-excitation spectroscopy in the visible region, often at sub-Doppler resolution by the technique of intermodulated fluorescence. After recording and assigning quantum number labels to the transitions observed in the spectra, we were able to accomplish several specific goals, including: (1) the determination of accurate values for the principal molecular constants by fitting parameterized molecular Hamiltonians to the measured transitions, (2) the characterization of the nature of the electronic states involved in the transition(s) using the analyzed hyperfine structure arising from Ta, Au and/or F nuclei, and (3) the determination of accurate transition frequencies that are of use to scientists in other fields. The results of our work on TaS and AuF have now been published in the physical chemistry literature via four different publications. We are in the process of preparing manuscripts describing our work on TaO and TaH. The work on AuS is very recent and is still in a preliminary stage. A substantial, broader impact of this work was to prepare Macalester chemistry majors for graduate work in physical chemistry and chemical physics, including students from underrepresented groups. A total of 13 different undergraduate students worked on this project. The skills these students acquired included the use of modern laser technology, methods of signal processing, computer interfacing of instrumentation, numerical data analysis, use of a machine shop, and the professional presentation of research results, all of which are skills that are extremely useful in a wide variety of scientific settings. Several of these students have now graduated from Macalester College. Of these alumni, three entered graduate school in chemistry, two entered medical school, and one entered an obstetrics program. Several other current and graduated students are planning on attending graduate school in chemistry. Two of these students are American students of color, where they will add to the diversity of the nation’s technical workforce.
