RESONANCE-ENHANCED 2-PHOTON IONIZATION SPECTROSCOPY OF RBCS IN A VERY COLD MOLECULAR-BEAM

Resonance enhanced two photon ionization spectrum of RbCs is obtained in a very cold pulsed molecular beam. We observe three vibrational series in the range of 540-590 nm. The excited electronic state that shows a very long vibrational series is assigned to the (4) (1) Sigma(+) state. The absolute vibrational quantum numbers are determined from the isotopic shift of the vibrational energy. Rotational constants of several vibrational levels are determined in comparison with the Fourier transform spectroscopic data reported previously. Another electronic state that shows a short and intense vibrational series is assigned to the (3) (II)-I-1 state and the vibrational quantum numbers are determined. The term values and vibrational frequencies of (RbCs)-Rb-85 are determined as T-e= 16 628.6 +/- 1 cm(-1) and omega(e)= 24.51 +/- 0.2 cm(-1) for the (4) (1) Sigma(+) state and T-e= 17 418.9 +/- 1 cm(-1) and omega(e)=22.53+/-0.2 cm(-1) for the (3) (II)-I-1 state.