A CNDO/2 study of σ- and π- relaxation energies and core electron binding energy shifts in some simple molecules

Abstract

Abstract A relaxation potential model has been used to study relaxation energies and shifts in core electron binding energies for some substituted alkenes and carbonyl compounds in terms of σ- and π-contributions. The conclusions from this study may be summarized as follows: (A) For the series R 1 R 2 C * CH 2 and R 1 R 2 C * O: (i) The total shifts vary in a regular manner, similar to the shifts in saturated systems; (ii) The variation in σ-relaxation energies is greater than the variation in π-relaxation energies. (B) For the series R 1 R 2 CCH 2 and R 1 R 2 CO: (i) There is little variation in the σ-relaxation energies; (ii) The π-relaxation energies show moderately large variations and the higher values are associated with unsaturated substituents which can donate π-electrons to the core-ionized atom via the conjugated π-system; (iii) The π-relaxation energies in the fluorinated systems are similar to those in the unsubstituted molecules; and (iv) The large -ve π-shift in the fluorinated systems results from a ground state build up of electron density at the site of core ionization.