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version cf benzene and the fluorocarbon vapor, respectively. Since photolysis often yields products closely related to those obtained by radioly~is,~ the work cited above suggested that similar valence isomerization might occur in radiolysis. (Radiationinduced cis-trans isomerization is well establi~hed.~) Results on the y irradiation of hexafluorobenzene (I) are reported here. Radiolysis of liquid or gaseous Il0in a Co60source at ambient temperature and at a dose rate of 7 X lo6 rads/hr yielded several products. These were separated by gas chromatography using diisodecyl phthalate and/or Kel-F oil column^.^ Liquid-phase irradiation yielded a fraction which had the same retention time as Dewar C6F6, hexafluorobicyclo[2.2.0]hexa-2,5-diene (11). This assignment was verified: the collected fraction showed the same infrared and mass spectra as Gas-phase authentic I1 obtained by phot~lysis.’~’~ radiolysis yielded two compounds with retention times similar to 11. Upon infrared and mass spectral analyses, these were identified as C6Fs, perfluorocyclohexadiene, and I. Since I and I1 have significantly different retention times, the C6F6 observed must be due to conversion of I1 a t the thermal conductivity detector.I2 This was confirmed by chromatography of small amounts of authentic 11; conversion to I also occurred. The valence isomer I1 was thus almost certainly produced in the gas phase and was unequivocally present in the liquid-phase irradiations. Vapor-phase photoisomerization to I1 requires
