Benzoyl radicals absorption spectrum

FIGURE 12.13 Absorption spectrum of benzoyl radicals obtained under photolysis of different precursors. 

Fig. 13 a Absorption spectrum of SCR 500 resin, which was major precursor material for two-photon photopolymerization in the work of Sun et al. [13, 14, 18-20] b Molecular structures of two kinds of benzoyl initiators BDMM and HCPA. c Typical reaction of radical production via an a-cleavage process. Radicals are produced in HCAP entirely by, and in BDMB mostly by, this mechanism. Note negligible single photon absorption at the working wavelength of 780 nm... 

Since the benzene emission in the thermal decomposition of benzoyl peroxide results from radical transfer by the phenyl component of a benzoyloxy-phenyl radical pair, phenyl benzoate produced by radical combination within the same pair should appear in absorption. A weak transient absorption has been tentatively ascribed to the ester (Lehnig and Fischer, 1970) but the complexity of the spectrum and short relaxation time (Fischer, personal communication) makes unambiguous assignment difficult. Using 4-chlorobenzoyl peroxide in hexachloro-acetone as solvent, however, the simpler spectrum of 4-chlorophenyl 4-chlorobenzoate is clearly seen as enhanced absorption, together with... 

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