A comparison of the oxygen 1s photoabsorption spectra of SO2 and NO2

Oxygen Is photoabsorption spectra of the bent triatomic molecules SO2 and NO2 have been measured at high resolution using synchrotron radiation. Spectra were assigned with the aid of X alpha and GAUSSIAN 94 calculations. Analysis of the spectra reveals similarities and differences in the electronic structure between SO2, which is classified as a hypervalent molecule and NO2 which is normally not classified as such. The spectral differences observed can be explained in terms of differences in the valence shell electron population and molecular geometry. There is no indication that the sulphur 3d orbitals play a significant role in the molecular bonding of SO2. The results support the interpretation that partial ionic bonding plays a greater role in the formation of hypervalent molecules than the promotion of electrons into the unoccupied d orbitals. (C) 2000 Elsevier Science B.V. All rights reserved.