CHIH-KAI LINHuang C.-L.Jiang J.-C.Chang A.H.H.Lee Y.T.Lin S.H.Ni C.-K.2022-10-122022-10-122002https://www.scopus.com/inward/record.uri?eid=2-s2.0-0037123253&doi=10.1021%2fja0120678&partnerID=40&md5=aca14f62730ec92ac91598c536ead79bhttps://scholars.lib.ntu.edu.tw/handle/123456789/623503The photodissociation of isotope-labeled toluene C6H5CD3 and C6H513CH3 molecules at 6.4 eV under collision-free conditions was studied in separate experiments by multimass ion imaging techniques. In addition to the major dissociation channels, C6H5CD3 ??C6H5CD2 + D and C6H5CD3 ??C6H5 + CD3, the respective photofragments CD2H, CDH2, and CH3 and their heavy fragment partners C6H4D, C6H3D2, and C6H2D3 were observed from C6H5CD3 dissociation. Photofragments 13CH3 and CH3, and their heavy fragment partners C6H5 and 13CC5H5, were also observed from C6H513CH3 dissociation. Our results show that 25% of the excited toluene isomerizes to a seven-membered ring (cycloheptatriene) and then rearomatizes prior to dissociation. The isomerization pathway competes with direct C-C bond and C-H bond dissociation. The significance of this isomerization is that the carbon atoms and hydrogen atoms belonging to the alkyl group are involved in an exchange with those atoms in the aromatic ring during isomerization. The dissociation rate of toluene at 193 nm is measured to be (1.17 �?0.1) ? 106 s-1.[SDGs]SDG6Photofragments; Chemical bonds; Imaging techniques; Isomerization; Molecular beams; Photodissociation; Toluene; alkyl group; toluene; article; chemical bond; chemical reaction kinetics; dissociation; isomerism; mass spectrometry; photochemistry; photolysisjournal article10.1021/ja01206782-s2.0-0037123253