CONTROL OF BOND DISSOCIATION VS IONIZATION (within the Sfb 450)The first experiments intended to control chemical reactions by using lasers were trying to break a certain chemical bond. Ever since, many experiments have shown that it is indeed possible to break bonds selectively in small molecules.Big molecules had to wait until Rabitz and Judson suggested an ingenious "optimal control" approach which was recently put into practice in the lab by Gerber and coworkers. The idea behind is that a computer programmed with genetic algorithms shapes iteratively a pulse, which is in this way optimized to perform a certain task. Yet, it is a bit mysterious how these "shaped-pulses" work. Can we extract any information from these pulses? Can we learn about the dynamics which such a pulse dictate to the molecule? In order to find out the answers to these questions and others, we have studied an organometallic complex - similar to the one first used in Gerber experiments - theoretically and experimentally. The experiments have been undertaken by Wöste and coworkers, producing a pulse which maximizes the parent ion hindering fragmentation. Can ab initio simulations reproduce it? We have computed ab initio potential energy surfaces for the fragmention and we have performed careful quantum dynamics to reproduce the pump-probe spectra from first principles. Only then, it was indeed possible to know which are the optimal conditions for a pulse which does not want to fragment the molecule but to increase the yield of the parent ion! See also Science 299, 536 (2003) and PRESS ECHO: Tagesspiegel, Optics.org , Chemie.DE |