Hydrogen migration and vinylidene pathway for formation of methane in the 193 nm photodissociation of propene:: CH3CH=CH2 and CD3CD=CD2

Photodissociation channels and the final product yields from the 193 nm photolysis of propene-h(6) (CH2CHCH3) and propene-d(6) (CD2CDCD3) have been investigated, employing gas chromatography, mass spectroscopy, and flame ionization (GC/MS/FID) detection methods. The yields of methane as well as butadiene relative to ethane show considerable variations when propene-h(6) or propene-d(6) are photolyzed. This suggests significant variances in the relative importance of primary photolytic processes and/or secondary radical reactions, occurring subsequent to the photolysis. Theoretical calculations suggest the potential occurrence of an intramolecular dissociation through a mechanism involving vinylidene formation, accompanied by an ethylenic H-migration through the pi-orbitals. This process affects the final yields of methane-h(4) versus methane-d(4) with respect to other products. The product yields from previous studies of the 193 nm photolysis of methyl vinyl ketone-h(6) and -d(6) (CH2CHCOCH3, CD2CDCOCD3), alternative precursors for generating methyl and vinyl radicals, are compared with the current results for propene.