Two-colour double resonance multiphoton ionisation spectroscopy of S-2

The S-2 radical has been studied in a pulsed molecular beam via two-colour multiphoton ionisation spectroscopy. This has resulted in the extended characterisation of the (3d pi)(3) Delta(g) Rydberg state, and of the first observation of an ion-pair state, a (5) Sigma(g)(-), state. The two-colour transition involved the mixed B/B'' states of the radical as the intermediate level of the ionisation scheme. The bands recorded showed sharp rotational structure, and spectroscopic constants from a rotational analysis of the spectra are presented.