 |
 |
 |
 |
 |
TITLE:
Molecular Dynamics and Real-Time Defect Formation in Table Salt
SPEAKER:
Professor Richard Williams,
TIME: Thursday Feb. 17, 2005 at 4 PM
PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)
Wake Forest University
Femtosecond time-resolved observations of the appearance of lattice defects after electronic excitation of NaCl as performed at Wake Forest and Osaka University have presented an interesting quandary: The yield of defects is temperature dependent, suggesting a Boltzmann process of thermal activation over an energy barrier. The trouble is, that the parameters that go into the Boltzmann model predict a formation time in serious disagreement with experiment. For example, the defect formation is observed to have gone to completion before even one period of the attempt frequency factor in the Boltzmann expression! The kicker is that when K. S. Song ran a molecular dynamics simulation, it reproduced the experiment in all regards, despite what our familiar concept of the Boltzmann model suggests! Picking apart the results of the computer experiment and the optical experiment side-by-side leads to an insight that may tie together this puzzle, an observation on hot luminescence made by Hanli Liu at WFU 13 years ago, another observation on "dynamic interstitials" by Itoh 30 years ago, and the cyclic recurrence of ice ages (according to Walter Robinson).