ChemInform Abstract: Minor Processes in the Photolysis of Azomethane at Low Pressure: An Upper Limit for the Rate of the Unimolecular Elimination of H2 from Vibrationally Excited Ethane

Abstract

The photolysis of azomethane in the near UV has been studied at room temperature and pressures from 10 mtorr to 10 torr. The main products, C2H6 and N2, accounted for more than 99% of the reaction. Minor hydrocarbon products observed were (with quantum yields) C3H8 (3.5 × 10−3), C2H4 (3.2 × 10−4), CH4 (3 × 10−3), and n-C4H10 (trace). Quantum yields of H2 of 4 × 10−5 and 2 × 10−5 were measured at azomethane pressures of 0.1 and 1.0 torr, respectively. The minor hydrocarbon products can be accounted for by reactions of CH3 and C2H5 radicals following hydrogen abstraction from azomethane by CH3. The H2 product observed represents an upper limit for the H2 elimination from vibrationally excited C2H6 formed by CH3 combination in the system, corresponding to a rate of elimination ca. 5 × 10−5 times the competing rate of dissociation to 2CH3. Assuming a frequency factor of 1013 s−1 for the H2 elimination, a lower limit of about 90 kcal mol−1 was estimated for the energy barrier.