Ultrafast multiphoton ionization dynamics and control of NaK molecules

The multiphoton ionization dynamics of NaK molecules is investigated experi mentally using one-color pump-probe femtosecond spectroscopy at 795 nm and intermediate laser field strengths (about 10 GW/cm(2)). Both NaK+ and Na+ i ons are detected as a function of pulse separation time, pulse intensities, and strong pulse-weak pulse order. To aid in the analysis, the potential e nergy curves of the two lowest electronic states of NaK+ and the electronic transition dipole moment between them are calculated by the GAUSSIAN94 UCI S method. Different ionization pathways are identified by Franck-Condon ana lysis, and vibrational dynamics in the A (1)Sigma(+) and 3 (1)Pi. states, a s well as in the ground state, is observed. Further, the existence of a hig hly excited (above the adiabatic ionization limit) neutral state of NaK is proposed. By changing the strong pulse-weak pulse order of the pulses, the ionization pathways for production of both ions can be varied and thus cont rolled. (C) 1998 American Institute of Physics. [S0021-9606(98)00448-6].