Ã2A′ » X̃2A′' emission spectrum of the HS2 radical

Abstract Chemiluminescence from electronically excited HS 2 radicals has been detected between 950 and 2100 nm in gas-phase flow systems. The emission essentially consits of ν 3 ′' sequences of the HS 2 (A 2 A′ » X 2 A′') transition with the 000 » 000 band origin at 1378 nm. DS 2 was also studied. For HS 2 the following spectroscopic constants (in cm −1 ) were deduced for the X 2 A′' state: ν 2 ′' = 904 ± 8, ν 3 ′' = 595 ± 4, and for the A 2′ A′ state: T 0 = 7255 ± 7, ν 3 ′ = 504 ± 4, A ′ A ′' = 9.7 ± 0.5. These data and relative band intensities are in excellent agreement with an ab initio SCF Cl calculation of Sannigrahi, Peyerimhoff and Buenker. As in spectra of HO 2 , forbidden Δ K = 0 transitions were observed which are not explained by axis-switching or Renner—Teller interaction mechanisms.