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Several resonance-stabilized radicals are observed as products of an electrical discharge containing p -cymene, a biogenic monoterpene that contributes to secondary organic aerosols after atmospheric oxidation. Three radicals are identified by resonant 2-color 2-photon ionization mass spectrometry, corresponding to loss of a methyl group or hydrogen atom from the parent p -cymene structure. The radicals are found to absorb in the spectral region consistent with a benzylic chromophore. The spectrum observed on m / z 119 is assigned to α ,4-dimethylbenzyl radical, and those on m / z 133 to the α , α ,4-trimethylbenzyl and p -isopropylbenzyl radicals, the latter two being intermediates in the atmospheric oxidation of p -cymene.

Photodissociation of CFClBr 2 + hν →CFCl has been shown to occur for λ 436±2 kJ mol −1 ). G3 Ab initio calculations were performed to provide estimates of Δ f H for CFClBr 2 , CFClBr, and CFCl, which were calculated to be −188±5, −43±5 and +30±5 kJ mol −1 , respectively. The dissociation energies (0 K) for sequentially breaking the C–Br bonds were calculated to be 257±5 and 183±5 kJ mol −1 , respectively. The energy required to break both C–Br bonds was calculated to be 440±5 kJ mol −1 , in excellent agreement with the experimental appearance threshold for CFCl. From the experimental appearance threshold, Δ f H (CFClBr 2 ) is estimated to be −184±5 kJ mol −1 .