Femtosecond laser spectroscopy on the vibrational wave packet dynamics of the A1Σ+ state of NaK

The vibrational wave packet dynamics of a heteronuclear diatomic alkali molecule in an excited state, the A1Σ+ state of gaseous NaK, has been measured for the first time. At λpump = 790 nm, a wave packet oscillation period of 442 fs and dephasing within 10 ps has been observed. This dynamics has been analysed by calculation of Franck-Condon factors and difference potentials. It is from this seen that initially the pump pulse prepares a wave packet at the inner turning point of the A-state. The wave packet then evolves in time and is probed at the outer turning point by a transition to the E-state with subsequent fluorescence detection.