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

Oxygen Is photoabsorption spectra of the bent triatomic molecules SO2 and N O2 have been measured at high resolution using synchrotron radiation. Spect ra were assigned with the aid of X alpha and GAUSSIAN 94 calculations. Anal ysis of the spectra reveals similarities and differences in the electronic structure between SO2, which is classified as a hypervalent molecule and NO 2 which is normally not classified as such. The spectral differences observ ed can be explained in terms of differences in the valence shell electron p opulation and molecular geometry. There is no indication that the sulphur 3 d orbitals play a significant role in the molecular bonding of SO2. The res ults support the interpretation that partial ionic bonding plays a greater role in the formation of hypervalent molecules than the promotion of electr ons into the unoccupied d orbitals. (C) 2000 Elsevier Science B.V. All righ ts reserved.