Two-colour double resonance multiphoton ionisation spectroscopy of S2

The S2 radical has been studied in a pulsed molecular beam via two-colour multiphoton ionisation spectroscopy. This has resulted in the extended characterisation of the (3dπ) 3Δg Rydberg state, and of the first observation of an ion-pair state, a 5Σg− 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.