A flash photolysis setup coupled to UV absorption spectrometry detection was used to measure the UV absorption spectra of the (CH 3 ) 2 (CH 2 O 2 .)CC(O)C(CH 3 ) 3 and (CH 3 ) 2 (CH 2 O 2 .)CC(O)CH 3 radicals between 207 and 290 nm. The self-reaction rate constants of these radicals were measured at 298 K:4.77 ± 0.35) × 10 −12 cm 3 molecule −1 s −1 , where quoted uncertainties only represent 2σ errors. Because of the similarities in both UV spectra and self-reaction kinetics between (CH 3 ) 2 (CH 2 O 2 .)CC(O)C(CH 3 ) 3 and (CH 3 ) 2 -(CH 2 O 2 .)CC(O)CH 3 radicals, it was suggested to extend this results to all (CH 3 ) 2 -(CH 2 O 2 .)CC(O)R peroxy radicals (with R = H, alkyl), arising from the chlorine-initiated oxidation of carbonyl compounds. This trend has been tested successfully in the case of the Cl-initiated oxidation of pivalaldehyde (Le Crâne et al.,