2-PHOTON RESONANCE-ENHANCED MPI-PES ABOVE THE LOWEST IONIZATION THRESHOLD - OBSERVATION OF THE [A (1)DELTA]5P-PI (2)PHI STATE OF THE SH (SD) RADICAL

A (2 + 1) resonance enhanced multiphoton ionization photoelectron spec troscopy (REMPI-PES) study of the hitherto unobserved [a (1) Delta]5p pi 2 Phi Rydberg state of the SH (SD) radical is reported. Despite the fact that this state has an excitation energy which exceeds the lowes t ionization energy, ionization is observed to occur preferentially by the absorption of a third photon after the two-photon excitation step , rather than through autoionization. Photoelectron spectra show a lar ge asymmetry in the rotational branching ratios, which is attributed t o the high value of Lambda(+) in the ionic state.