Reaction product identification from O(3P)+benzene, toluene, and 1,3,5-trimethylbenzene collisions in crossed molecular beams

Abstract

Although absolute rate coefficients have been measured for a number of reactions of aromatic molecules with O(3P) atoms, very little is known about the mechanisms of these reactions. In order to identify the products of O atom–aromatic molecule reactions, the products of single reactive collisions between oxygen atoms and benzene, toluene, and 1,3,5,-trimethylbenzene have been observed in crossed molecular beam experiments. The products were detected with a quadrupole mass spectrometer. Two product paths were observed for O+benzene: (1) the O atom–benzene adduct, which is most likely phenol, and (2) carbon monoxide and a C5H6 hydrocarbon which is probably 3-penten-l-yne. An additional path involving the formation of (methyl-substituted) benzaldehyde and H2 was observed for the reaction with methyl-substituted benzenes. Only the adducts, the benzaldehydes, and the olefins were observed directly. The identities of the corresponding products were inferred from the difference between the mass-to-charge ratio of the observed product and that of the C6H6O, C7H8O, and C9H12O adducts. Arguments based on electronic state symmetry indicate that the carbon monoxide-olefin path involves the decomposition of vibrationally excited phenol in its ground electronic state. This state is reached by a spin-forbidden transition from the triplet reactant state. The benzaldehyde products can be explained by a mechanism analogous to one of the reaction paths of O(3P)+ethylene.

Crossed-Beam and Theoretical Studies of the O(3P, 1D) + Benzene Reactions: Primary Products, Branching Fractions, and Role of Intersystem Crossing

“…It is appropriate here to comment on the nature of the coproduct of the spin-forbidden CO-forming channel. Clearly, the early suggestion 37 that the coproduct of CO is the open chain hydrocarbon 3-penten-1-yne was erroneous, as demonstrated by the present and previous theoretical work, 24 , 48 , 51 by the direct observation of cyclopentadiene in the experiment by Taatjes et al 24 through accurate measurements of the ionization efficiency curve of the product, and also by the present and previous 10 , 51 CMB studies.…”

Theoretical Reinvestigation of the O(3P) + C6H6 Reaction: Quantum Chemical and Statistical Rate Calculations

“…Figures 10 and 11 also show that the products c-C 5 H 6 + CO, phenol, and benzene oxide/oxepin are major, at least in some conditions, while the products phenoxy radical + H, c-C 6 H 4 + H 2 O, the ketone S3 and BDK S8 are always minor. These results are in agreement with earlier experimental observations for key products such as phenol and CO. [19][20][21] As can be seen, the fractions of the various products depend in a complex way on T and P. In general, an increase of temperature enhances the yields of c-C 5 H 6 + CO, phenoxy radical + H, and c-C 6 H 4 + H 2 O. On the other hand, increasing the pressure will reduce the yields of c-C 5 H 6 + CO, phenoxy radical + H, and c-C 6 H 4 + H 2 O, but increase those of phenol and benzene oxide/oxepin.…”

Dynamics of reactions O(D1)+C6H6 and C6D6

“…Several experimental [36][37][38][39][40] and theoretical 41,42 investigations on reactions of O͑ 3 P͒ with aromatic compounds have been reported. Sibener et al 36 investigated the reaction of O͑ 3 P͒ +C 6 H 6 with crossed-molecular beams and concluded that the initially formed triplet biradical C 6 Barry et al 38 investigated the reaction of a crossedmolecular beam of O͑ 3 P͒ +C 6 H 6 at a collision energy of 16.5 kcal mol −1 and reported little ͑0.8 kcal mol −1 ͒ rotational excitation of the OH product detected by LIF; the results indicate that the reaction might proceed directly via an OϪHϪC collinear transition structure.…”