LASER SPECTROSCOPY OF MOLECULAR-IONS - THE A-X TRANSITION IN THE OCS RADICAL-CATION

Spectroscopy of the OCS+ ion in its ground and first excited states ha s been performed over a wide energy range using one-photon dissociatio n spectroscopy. We used multiphoton ionization in the first step for s tate selective ion preparation in single well-defined vibrational and spin-orbit states. This simplifies the ion spectra of the transition t o the first excited A state considerably and thereover delivers the in formation of the ion ground state by using hot ion preparation. For th e stretching vibrations anharmonicities have been observed and for the first overtone of the bending vibration Fermi resonances have been fo und. Rotational constants could be determined for the vibrational grou nd states of the X and A ionic states in both spin-orbit components. A new double resonance technique was applied to measure vibrational fre quencies in the ionic X ground state.