A study of the S 2(X 3Σ −g) molecule by multiphoton ionization spectroscopy

Abstract

In this work the S 2 molecule has been studied using resonance enhanced multiphoton ionization (MPI) spectroscopy in the single-photon wavelength region 285–320 nm. This has resulted in the first spectroscopic observation of a gerade Rydberg state of S 2. The observed bands, which show spin—orbit structure, have been assigned to a two-photon resonant process, 3Δ g(3dπ←X 3Σ − g. Transitions to three vibrational levels (ν′ = 0, 1, 2) of the excited state have been recorded. This has enabled determination of vibrational constants ( ω e and ω eχ e) and the spin—orbit coupling constant of the 3Δ g state, whilst rotational constants ( B ν′) were derived from band head separations. A band in the MPI spectrum of S 2 corresponding to the one-photon resonance B 3Σ − u, ν′=8←X 3Σ − g, ν″=0 has also been observed. This has been detected in both the S + 2 and S + mass channels. Possible mechanisms for production of these ions via the B 3Σ − u state are discussed.