Chemiluminescence of S2 in solid argon

Upon slow warming of previously photolyzed matrix samples of OCS/Ar, CS2/Ar, OCS/Kr, and OCS/SF6 (M/R=100), the B (B″) →X chemiluminescence of S2 is observed as reported earlier. In addition, two new progressions were recorded, a weak progression between 5580–6890 Å and a stronger one between 6680–8750 Å. With OC34S, the 6680–8750 Å progression displayed isotopic shifts that allow deduction of νoo=15 750±10 cm−1, ω″e=699±5 cm−1, and ωexe″=2.6±1 cm−1. Similarly, the weaker 5580–6890 Å progression corresponds to νoo=20 870±30 cm−1, ω″e=724±6 cm−1, and ωex″e=2.9± 1 cm−1, with a less favored, alternative vibrational assignment that gives νoo=21 600±30 cm−1, ω″e=731±6 cm−1 and ωex″e=2.9±1 cm−1. These spectroscopic parameters point to assignments of the c1Σ−u→a1Δg and A′3Δu →X3Σ−g transitions of S2 for the 6680–8750 Å and 5580–6890 Å emissions, respectively. These are the first observations of these transitions of diatomic sulfur, and one of them provides the first direct spectroscopic information illustrating that the c1Σ−u state (To=20 250±200 cm−1) actually lies lower than the A3Σ+u and A′3Δu states, as is the case for O2.