EPR study of the radicals involved in the photooxidation of ethylene on TiO

The photooxidation at 77 K of C2H4 on either chlorine free or chlorinated TiO2 (rutile) samples produces two radicals with the following g tensors : chlorine free surface (species A) g1 = 2.035, g2 = 2.008, g3 = 2.001 ; chlorinated surface (species B)g1 = 2.035, g2 = 2.008, g3 = 2.003. The change in the EPR spectra on using C2D4 or 13C2H4 indicates that species A and B contain hydrogen and carbon. On the other hand, species A and B can also be obtained by using 17O enriched oxygen. The presence of lines from two non equivalent oxygen nuclei both labelled with 17O confirms that alkyl peroxy radicals ROO* are formed. For species A, the 17O hyperfine tensor is found to be : [math] = 95 G, [math] = 35 G, A1 [math] A2 — 0 G, while for species B, the 17O hyperfine tensor is [math] = 94 G, [math] = 36 G, A1 [math] A2 [math] 0 G. The nature of the alkyl part of the radical is discussed for species A and B