Controlling the femtochemistry of Fe(CO)(5)

We report on active control of the femtosecond photodissociation and ioniza tion reactions of iron pentacarbonyl, Fe(CO)(5), in the gas phase. The spec tral phase of femtosecond laser pulses is modified in a pulse shaper, emplo ying a learning evolutionary algorithm, Direct feedback from the experiment is used to iteratively improve the laser pulse shape according to a given optimization problem. This many-parameter optimization is compared with one -parameter control schemes and found to be more versatile, because it can s ample a much more general search space. Information about the underlying re action mechanism can be extracted from the results of the automated optimiz ation. It is further shown that second-harmonic generation (SHG) can be use d at the output of a 800 nm pulse shaper to implement 400 nm excitation exp eriments. The optimization procedure not simply increases the SHG efficienc y but optimizes the objective given for the combined system of SHG and Fe(C O)(5) photochemistry. The importance of the choice of fitness function is e xamined experimentally. By choosing appropriate weighting factors, it is po ssible to tune the optimization results from an optimization of the ratio o f photoproduct yields toward optimization of the absolute photoproduct yiel ds. Evolutionary laser pulse shaping is considered a very useful tool for u nraveling the processes of photoinduced chemical reactions.