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Cross-disproportionation/combination ratios for CFH2 and CF3 with C2H5 radicals have been determined to be A = 0.032 f 0.012 and A = 0.098 f 0.020, respectively, over the temperature range 25-75°C. For the pathway that yields CFH and CzHs, A = 0.020 f 0.005 a t 25°C.

The photochemistry of azo-n-propane is investigated a t 366 nm up to 1 atm pressure, and over a range of temperature from 50 to 190OC. Some additional experiments with azoethane a t room temperature and azoisopropane a t 180 and 190°C are also reported. From a consideration of the pressure dependence of the quantum yields for photodissociation a generalized mechanism is proposed which accounts for the known experimental observations in acyclic azoalkane photochemistry. These observations include the extensive photoisomerization data which were previously obtained for azoisopropane. In the mechanistic scheme dissociation a t low pressures is believed to occur mainly from Sy and Ty, the vibrationally excited and randomized first excited singlet and triplet states. A t high pressures and low temperatures (5 100°C) the major dissociation channel is probably a nonrandom SI state.In direct or singlet sensitized photolysis isomerization occurs predominantly at high pressure and is postulated to occur by internal conversion from S:, the thermalized singlet, to the ground state. During the process partitioning to the cis or trans isomer is equally probable. In triplet sensitized photolysis isomerization occurs via intersystem crossing from TI to the ground state. A t elevated temperatures (>150°C) dissociation from Sy, which has a significant activation energy, can compete with return to the ground state.

The photochemistry of azoethane and hexafluoroazornethane at 366 nm has been reinvestigated up t o 1 atni pressure, and over a range of temperature from 27 to 150°C. The Stern-Volnier type quenching plots primarily demonstrate the decomposition of a single electronic and vibrationally excited state for azoethane, but competitive photodissociation from two different electronic and vibrationally excited states, which was previously postulated for hexafluoroazomethane and azoisopropane, is confirmed for hexafluoroazomethane. I t is concluded, however, that two different electronic and vibrationally excited photodissociating states are present in azoethane photolysis, but that one of them is difficult to detect, a t least by the present approach.Photosensitization with biacet,yl a t 436 nni also causes the dissociation of azoethane, and this is probably from the vibrationally equilibrated first triplet state. The energy barrier for this process was found to be 5.0 kcal/mol.

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