COLL 344 |
| Victoria Buch, Department of Physical Chemistry, Hebrew University, The Hebrew University, Jerusalem, 91904, Israel and Jan K. Kazimirski, Max-Planck-Institut fuer Stroemungsforschung, Bunsenstr. 10, 37073 Goettingen. |
| The study focuses on structure and vibrational spectra of icy particles. Ice nanoparticles display distinct structural and spectroscopic characteristics for the surface and for the interior (Devlin, Joyce and Buch, J. Phys. Chem. A 104, 1974 (2000)). Computational search for low energy structures of (H2O)n particles was carried out in the size range of tens - hundreds of molecules. The optimization procedure combined temperature dependent classical trajectories, hydrogen network improvement, and optimization by Diffusion Monte Carlo. Up to n~100, the final lowest energy structures found were compact, 3-dimensional, and amorphous. In contrast, for n=293 and 931, the lowest energy structures included a largely crystal core, and an amorphous surface. The ice crystal structure is favorable for the interior rather than for the surface, and therefore a minimal cluster size is required for crystallinity. The surface adopts a non-crystalline amorphous structure with enhanced population of 5- and 4-membered water rings, which allow for reduction in the population of under-coordinated surface molecules. The above structural evolution is in accord with evidence from IR spectra. The computed structures are used to interpret recent measurements of size-dependent OH stretch spectra of ice particles of the groups of Devlin et al., Buck et al., and Bauerecker et al. |
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Vibrational Analyses of Dry and Wet Surfaces
2:00 PM-5:30 PM, Tuesday, March 30, 2004 Marriott -- Grand Ballroom H, Oral
Division of Colloid and Surface Chemistry |