From the atmosphere to the interstellar medium: Long-range molecular interactions

Understanding real chem. systems almost always involves studying the interactions between a large no. of mols. and atoms. Theor. and computational chem. are powerful tools that provide atomistic insight into systems that can be difficult to study any other way. We will briefly discuss how we exploited these techniques in the past to investigate the chem. physics of clusters in the atm. In addn., computational studies are necessary to explain new measurements when there is not a deep body of literature to help with the interpretation. In the condensed phase, the THz (or far- IR, from 0.1 to 10 THz or 3 to 330 cm ) region of the electromagnetic spectrum is sensitive to long- range, weak interactions of many mols. In solids, this corresponds to low- energy phonon modes. In liqs., such as water, the hydrogen- bond dynamics dominate the THz spectrum. Consequently, these THz- active modes are sensitive to small changes in the structure of the material. However, the current body of literature on these modes is small enough that interpretation of new spectra requires significant quantum chem. calcns. This talk will discuss THz lab. spectra of mol. solids, or ices, of astrochem. interest. Recent theor. results, and our own calcns. have allowed us to understand how the changes in the spectrum correspond to changes in the structure of the ice. These structural changes may have important implications for diverse systems such as: the chem. of the interstellar medium, hydrogen- bond dynamics in liqs., and biol. systems