The radiation produced in an afterglow due to the reaction of Ar(P-3(0,2)) with SO2 has been studied between 230 and 600 nm. Two progressions are assigned to SO species. Aside from SO (c(1)&USigma;-→ X-3&USigma;(-) ), a new SO emission band located closely to the peak lines of SO (c(1)&USigma;(-) → X-3&USigma;(-)) in the range of 400 and 600 nm was also discovered and assigned to the SO (A(n3)&USigma;(+) → X-3&USigma;(-)) transition. A set of spectroscopic constants for the A(n3)&USigma;(+) state was deduced as T-00 = 30460 ± 18.0 cm(-1), ω'(e) = 685 18.0 cm(-1), ω'(e)χ'(e) = 7.7 ± 0.8 cm(-1). © 2005 Elsevier B.V. All rights reserved.