The adiabatic flash photolysis of NO2 and SO2

The well known temporary disappearance of the SO2 spectrum following flash photolysis under adiabatic conditions has been shown to be an optical illusion induced by temperature broadening of the banded structure. A similar phenomenon has been observed for NO2 following flash irradiation with wavelengths above 400 nm . The two spectra previously ascribed to a thermal isomer of SO2 have otherwise been accounted for. The first, a continuous absorption below 240 nm , is the result of temperature broadening of the (C–X1A1) system of SO2 and the other, a series of bands in the 180 nm region, belongs to one of two new triplet systems of SO (D3II–X3∑– and E3II–X3∑–). These two systems of SO fit a Rydberg series for an ionization potential of 9.8 eV.