Chemiluminescence of S2 in solid argon

Abstract

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 ν_oo=15 750±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 ν_oo=20 870±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 ν_oo=21 600±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 c¹Σ⁻_u→a¹Δ_g and A′³Δ_u →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 (T_o=20 250±200 cm⁻¹) actually lies lower than the A³Σ⁺_u and A′³Δ_u states, as is the case for O₂.