Laser spectroscopy of 3A2 -> 1A1 phosphorescence of sulphur dioxide

Abstract

Supersonic jet beam of SO₂ seeded in Ar was excited by 3021A laser radiation and the resulting luminescence spectrum was recorded in the 3060-5000A range. At very low SO₂ concentration two different phosphorescence spectra were distinguished from the F-band resonance fluorescence spectrum when proper optical alignment was used. One phosphorescence spectrum was recognized as the ³B₁-->¹A₁ band system while the second was assigned as the previously undetected ³A₂-->¹A₁ band system. The distinction between the two band systems was based mainly on the observation that each system reached vibrational equilibrium at SO₂ pressure different from the other. Five progressions of energy separation 955 cm⁻¹ were identified as V₁ progressions of ³A₂ state. The zero order values for V₂ is around 417cm⁻¹ is around 1062 cm-¹, on the other hand, were estimated from a tentative vibrational analysis of the resulting ³A₂-->¹A₁ phosphorescence spectrum. The formation mechanism of the triplet molecules and the possible internal conversion between the ³A₂ and ³B₁ states are also discussed.