Competition of different ionization pathways in K-2 studied by ultrafast pump-probe spectroscopy: A comparison between theory and experiment

We present a comparison of experiment and theory of ultrafast one-color pum p-probe multiphoton ionization spectrocopy of K-2. The wave packet propagat ion in the A (1)Sigma(u)(+) state and in the (2) (1)Pi(g) Rydberg state is monitored in detail by changing systematically the pump and probe wavelengt h from 779 nm to 837 nm. The measured total ionization rates as a function of the delay time between pump and probe are shown to depend sensitively on the pump and probe wavelengths used and exhibit drastic changes and a vari ety of fascinating structures as the direct observation of inward and outwa rd wave packet detection and frequency doubling of the detected wave packet oscillation. The time dependent quantum mechanical wave packet calculation s are in excellent agreement with the experimental results and allow a clea r interpretation of different ionization pathways and mechanisms observed i n the femtosecond ion signal. (C) 1999 American Institute of Physics. [S002 1-9606(99)01240-4].