Femtosecond spectroscopy of the (2) (1)Sigma(+)(u) double minimum state of Na-2: Time domain and frequency spectroscopy

Femtosecond time resolved pump-probe wave packet dynamics in the (2) double minimum state of Na-2 are reported. The experiments were performed in a molecular beam with ion Time of Flight (TOF) detection. By Fast Fourier Transformation (FFT) of the observed time domain data the energy spacings of the coherently coupled vibrational levels in the (2) 1 Sigma(u)(+) potential are obtained with an accuracy of 0.02 cm(-1), although an ultrafast laser source with its inherent spectral width was used in the experiment. The wavelengths of the pump and probe laser pulses are chosen such that in this two color experiment we can control ionisation versus ionisation induced fragmentation. In order to study the influence of the potential barrier on a vibrational wave packet motion we performed simulations based on time dependent quantum calculations.