Competition of different ionisation pathways in K/sub 2/ investigated by fs pump and probe spectroscopy: experiment and theory

Summary form only given. During the last decade both, experimentalists and theoreticians, began extensively to investigate ultrafast phenomena as wave packet propagation, coherent control, internal vibrational redistribution, structural relaxation and photodissociation in physical, chemical and biological systems. In particular, the wave packet propagation of small molecules as the potassium dimer are studied in great detail. Recent studies of this molecule focused on the ionisation step in ultrafast pump and probe experiments, applying fs-multiphoton ionisation spectroscopy. In these schemes the pump pulse prepares a wave packet in both the A/sup 1//spl Sigma//sub u//sup +/ and (2)/sup 1//spl Pi//sub g/ state at the inner turning point by means of a one or two-photon process. The delayed probe pulse can transfer the wave packet to an ion state by another two or one photon process. The generated ions are detected mass-selectively. We show, that it is possible to control the transition of the wave packet by changing the applied wavelength of the probe pulse. Two features appear in this context: first the transition pathway can be shifted within the same potential energy surface or, second, in such a way that the ionisation proceeds via different electronic surfaces.