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Minor processes in the photolysis of azomethane at low pressure: An upper limit for the rate of the unimolecular elimination of H 2 from vibrationally excited ethane
Author(s) -
Roscoe J. M.,
Blatt C.,
Back R. A.
Publication year - 1991
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550230708
Subject(s) - chemistry , photodissociation , torr , radical , dissociation (chemistry) , excited state , hydrogen atom abstraction , hydrocarbon , hydrogen , photochemistry , branching fraction , analytical chemistry (journal) , atomic physics , organic chemistry , thermodynamics , physics
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, C 2 H 6 and N 2 , accounted for more than 99% of the reaction. Minor hydrocarbon products observed were (with quantum yields) C 3 H 8 (3.5 × 10 −3 ), C 2 H 4 (3.2 × 10 −4 ), CH 4 (3 × 10 −3 ), and n ‐C 4 H 10 (trace). Quantum yields of H 2 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 CH 3 and C 2 H 5 radicals following hydrogen abstraction from azomethane by CH 3 . The H 2 product observed represents an upper limit for the H 2 elimination from vibrationally excited C 2 H 6 formed by CH 3 combination in the system, corresponding to a rate of elimination ca. 5 × 10 −5 times the competing rate of dissociation to 2CH 3 . Assuming a frequency factor of 10 13 s −1 for the H 2 elimination, a lower limit of about 90 kcal mol −1 was estimated for the energy barrier.