This project, supported by a grant to Professors Cherice M. Evans (Queens College - CUNY) and Gary L. Findley (University of Louisiana at Monroe) from the Chemical Structure, Dynamics, and Mechanisms Program of the Division of Chemistry, explores the interactions between solutes in a near critical point supercritical fluid (SCF). The experiments will employ a synchrotron radiation source (e.g., University of Wisconsin Synchrotron Radiation Center) to measure the ionization energies of dopant molecules within the fluid at various electric field strengths and fluid number densities. The results from these studies will yield the minimum energy of the conduction band, which will be compared to predicted values obtained from the local Wigner-Seitz model. Monte Carlo and molecular dynamics simulations will also be used to investigate the energy of a trapped electron in these same near critical point fluids.
The use of supercritical fluids and near critical point fluids as a highly tunable solvent for the synthesis of high purity nanoparticles and pharmaceuticals is an emerging area of technology. This research will advance our understanding of critical point fluids in general and, therefore, will provide insights for those who seek to develop chemical reactions in near critical point SCFs. The research program will engage both graduate and undergraduate students at CUNY and ULM. A Research Experiences for Undergraduate (REU) activity will be integrated into the synchrotron radiation facility experiments.
CHE-0956719 funds were employed to support research that led to the development of a new experimental technique, namely field enhanced photoemission (FEP), to measure the quasi-free electron energy in dense and near critical point fluids. FEP was then used to measure, for the first time, the quasi-free electron energy in neon, helium, hydrogen, deuterium, nitrogen, oxygen and carbon monoxide, from low density to the density of the triple point liquid. Thus, these studies represent the first comprehensive investigation of the quasi-free electron energy in diatomic fluids from low density to the density of the triple point liquid, at noncritical temperatures and on a near critical isotherm, as well as the completion of the measurement of the quasi-free electron energy in all of the rare gases. (We had previously measured the quasi-free electron energy in dense argon, krypton and xenon.) These experimental data were used to extend the local Wigner-Seitz model – a theory developed by us to model accurately the quasi-free electron energy in the rare gases argon, krypton and xenon – to fluids with positive zero-kinetic-energy electron scattering lengths (i.e., the repulsive fluids neon, helium, hydrogen, deuterium and nitrogen). The ongoing analysis of the quasi-free electron energy in carbon monoxide will begin the extension of the local Wigner-Seitz model to polar fluids. If this extension is successful, then the local Wigner-Seitz model will mark the first broad ranging theory of the quasi-free electron energy that is accurate to within 0.3% of experiment at noncritical temperatures and 0.5% of experiment near the critical isotherm of the various fluids. The increased understanding of the influence that the local density and its fluctuations have on the quasi-free electron energy in dense fluids through the local Wigner-Seitz model is now leading to the development of new theories for electron mobility in dense fluids. The detailed knowledge of the quasi-free electron energy also yields fundamental insights into the role that density plays in chemical reaction dynamics. The collaboration between Dr. Cherice Evans (Co-Principal Investigator, Queens College – CUNY) and Dr. Gary L. Findley (Co-Principal Investigator, University of Louisiana at Monroe) permits undergraduate students from rural Louisiana to interact with those from New York City, thereby broadening the perspective of both groups of students. The Research Experience for Undergraduate supplement support ten students (50% of whom are from under-represented groups in the sciences). Of these students, five students matriculated into graduate programs in chemistry or biochemistry, one student has been accepted into the B.A./M.A. program in chemistry at Queens College – CUNY, one student went to medical school at SUNY Downstate Medical University, two student are in the process of applying to Ph.D. programs in chemistry during the 2013–2014 academic year, and one student is a junior in chemical biology at the University of Louisiana at Monroe with plans on applying to Ph.D. programs in either chemistry or physics. The Ph.D. student, who was supported in part from this grant, mentored many of these undergraduate students and, therefore, developed a remarkable ability to communicate complex experimental techniques, data analysis skills and theoretical methods to advanced undergraduate research students. This student defended his dissertation in April 2013, thereby completing his degree in four years. The research supported by this grant yielded 11 papers directly related to the research. Six of these papers have been published in peer reviewed journals, one paper has been submitted to a peer reviewed journal, and four papers are currently in preparation for submission to peer-reviewed journals. This research also yielded a Ph.D. dissertation on the quasi-free electron energy in repulsive fluids, and four papers from undergraduate research projects that are currently in preparation for submission to peer reviewed journals but are not directly related to the work on the quasi-free electron energy in near critical point fluids. (These non-related research projects were used as part of the selection process for undergraduate research students who participated in the studies of the quasi-free electron energy.)
