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 ν₀₀ = 15750±10 cm^-1, ω″_e = 699 ± 5 cm^-1, and ω_ex_e″ = 2.6 ± 1 cm^-1. Similarly, the weaker 5580-6890 Å progression corresponds to ν₀₀ = 20870 ± 30 cm^-1, ω″ _e = 724 ± 6 cm^-1, and ω_ex″ _e = 2.9 ± 1 cm^-1, with a less favored, alternative vibrational assignment that gives ν⁰⁰ = 21600 ± 30 cm ^-1, ω″_e = 731 ± 6 cm^-1, and ω_ex″_e = 2.9 ± 1 cm^-1. These spectroscopic parameters point to assignments of the c ¹Σ _g^-→a ¹Δ_g and A′ ³Δ_u → X ³Σ_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 c ¹Σ _u^-l state (T₀ = 20250 ± 200 cm ^-1) actually lies lower than the A ³Σ _u⁺ and A′ ³Δ_u states, as is the case for O₂.