The effect of temperature on the ultraviolet spectrum of sulfur dioxide has been studied over the temperature range 20 to 1000 °C. The equilibrium constant for the reaction[Formula: see text]where (SO2) is an isomeric form or an excited state of sulfur dioxide, has been obtained at several temperatures. The enthalpy change for the transition was found to be 4.1 ± 0.4 kcal mole−1.