In this award, funded by the Chemical Structure, Dynamics and Mechanisms Program of the Chemistry Division, Prof. Michael C. Heaven of Emory University and his research group will investigate unusual bonding mechanisms in (1) beryllium clusters containing 3 - 30 Be atoms, and (2) the interactions between beryllium oxide (BeO) and rare gas atoms (helium, neon and argon). The ultimate aim of these studies is to develop a better understanding of the unusual modes of bonding that are not well-characterized in terms of conventional models, and to advance our understanding of bonding when clusters grow from a few atoms in size to large systems that approach bulk metal behavior. The BeO rare gas studies will address intriguing theoretical results that predict unusually strong bonds involving normally inert rare gas elements. A variety of experimental tools will be employed, including photodetachment spectroscopy, laser-induced fluorescence, resonance-enhanced multiphoton ionization, and cavity ring-down spectroscopy.
The results from these studies will help chemists to develop a deeper understanding of bonding that encompasses the traditional models of bonding as well as the unusual interactions that are one of the themes of the present study. The research will provide the graduate and undergraduate students, and post-doctoral associates involved with a rich experience in advanced experimental and theoretical methods. A collaboration will be established with Spelman College, to expand the research experience to students from a historically Black women's college.
Bond formation is a central concept in chemistry, so the influence of research that enhances our understanding of the subtleties of bonding can be far reaching. Computational models of chemical bonds are used extensively in the design of new materials, synthetic pathways and catalysts. While these models are often capable of making accurate predictions, there are certain modes of bonding where the models yield unreliable results. The chemical properties of the element Beryllium provide many examples of bonds that are not adequately described as either ionic or covalent bonds. For these bonds, the details of how the motions of the electrons are coordinated are critically important. As computational models for this problem are developed (for application to all elements), it is essential to have accurate experimental data that can be used to assess and benchmark the theoretical tools. The aim for this program has been to obtain definitive structure and bonding information for prototypical Beryllium compounds. The interactions between Be atoms provide an excellent starting point for examining unusual bonding mechanisms. Although the bulk metal is a hard, high-melting point substance, the bond between an isolated pair of Be atoms is so weak that the Be2 molecule is not stable at room temperature. Our studies of this simple diatomic molecule have shown that the bond strength increases by more than a factor of 20 when one electron is removed to form the Be2+ ion. Calculations, validated by comparing with the properties of Be2 and Be2+, show that the bond strength increases rapidly in going from Be2 to Be3, in a markedly non-additive fashion. The hypermetallic compound BeOBe presents another unusual bonding situation. As both BeO and Be have completed electron shells, basic molecular orbital theory predicts that there will be little in the way of a bonding interaction for the second Be atom. Our measurements showed that BeOBe is quite strongly bound, with a linear symmetric structure. For this species, removing an electron had only a minor effect on the bond strength. Large-scale electronic structure calculations were successful in predicting the properties of BeOBe and explaining the origin of the bonding. Be is the lightest member of the group of alkaline earth metals (group IIa). The known alkaline earth hydroxides (MOH) are linear species with ionic M-O bonds. In contrast, computational models for BeOH predict a bent structure with appreciable covalent bonding. We have been able to validate the models by obtaining the first structural information for BeOH and the isotopologue BeOD. Other Be compounds studied in this program included Beryllium Carbide (BeC) and hypermetallic Ben+1On clusters. Theoretical models were developed that explain the bonding mechanisms that are dominant is these molecules. In terms of education and outreach, the broader impact (beyond that of the usual training of graduate students and postdoctoral fellows), was ito increase the participation of African American women, which is a notably underrepresented group in the physical sciences. This was accomplished through a collaboration with Spelman College in Atlanta. Spelman, a historically black, liberal arts college for women, has become one of the leading institutions in preparing African American women for careers in science, engineering and mathematics. However, as Spelman does not have a PhD program in chemistry, the research opportunities are limited. To address this need, a program was developed that provides jointly mentored research experiences for Spelman students at Emory.
