Basic Research Needs for Geosciences - Energetics Meetings and ...

CROSSCUTTING ISSUE:THERMODYNAMICS OF THE SOLUTE-TO-SOLID CONTINUUMclusters that change the local chemistry in a way that cannot be accounted for by surfacecomplexation models. Such clusters may be the precursors to surface precipitates.A concerted approach using a variety of modeling studies and experiments defining structures,thermodynamics and reactivity is needed to provide the basis for a thermodynamic description ofthe gradational regime between solutes and solids. The molecular scale insights derived frommodern spectroscopic techniques must be accounted for in this description. The computationalchallenge is in both the computing power and algorithms for dealing with systems containingmore than a few hundred atoms. The experimental challenge is to attain higher resolution inconcentration, space, and time for the study of structures and their evolution. To further theseends, large facilities must be developed and exploited, including large parallel processors, newtechniques at light sources, and new capabilities at neutron-scattering facilities.SCIENTIFIC IMPACTSA unified fundamental description of the transition from isolated molecules in solution toextended solids has a wide range of implications from physics and chemistry, to material science,biology and earth science. What is sought is a description of chemical thermodynamics that doesnot rely on a sharp distinction between solutes and solids. The impact of a new paradigm will beas wide as the present range of application of chemical thermodynamics. In terms of kinetics, adescription of the full diversity of chemical states and local environments will lead to areformulation of rate laws for chemical transformations. Rather than focusing on averageproperties, this approach will identify the energy landscapes through which reactions will occur.TECHNOLOGY IMPACTSIn addition to developing an enhanced capability to predict the migration of radionuclides andother components in natural systems, there are increasing opportunities to use nanotechnology inmonitoring subsurface environments. When nanoscale or molecular sensors (as passive tracers,as active sensors for changes in pH or redox fronts, or as “smart sensors” which are attracted to“hot spots”) are placed in the environment, they become part of the geologic system. Theirtransport and survival in the harsh environment, and their potential role as contaminants ortransporting agents for other contaminants, must be characterized. Such characterization willinvolve many of the same thermodynamic and kinetic issues described above.168 Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems