Two-photon resonance enhanced MPI-PES above the lowest ionization threshold. Observation of the [a 1Δ]5pπ 2Φ state of the SH (SD) radical

A (2 + 1) resonance enhanced multiphoton ionization photoelectron spectroscopy (REMPI-PES) study of the hitherto unobserved [a 1Δ]5pπ 2Φ Rydberg state of the SH (SD) radical is reported. Despite the fact that this state has an excitation energy which exceeds the lowest 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 large asymmetry in the rotational branching ratios, which is attributed to the high value of Λ+ in the ionic state.