Spectrum of SO: Analysis of the B 3 Σ − – X 3 Σ − and A 3 Π– X 3 Σ − band systems

The absorption spectrum of SO radicals produced by flash photolysis of a mixture of COS + O 2 + Ar is investigated. A partial rotational analysis of the previously known bands of the B 3 Σ − –X 3 Σ − transition which lie in the region of 1900 to 2400 Å is presented, and the predissociations and perturbations of the B 3 Σ − state are discussed. A complex red-degraded band system near 2500 Å, previously observed in emission and attributed to SO 2 , is shown to be due to a 3 Π–X 3 Σ − transition of the SO molecule. Effective rotational constants of the 3 Π state are derived from the analysis of these bands photographed at high resolution. In order to obtain the vibrational numbering of the 3 Π–X 3 Σ − bands, these were also photographed in emission from a microwave discharge through a mixture of S 18 O 2 + S 16 O 2 . A general discussion of the currently known states of the SO molecule is given.