Selected ion flow tube studies of air plasma cations reacting with alkylbenzenes

Journal Article · Thu Feb 10 04:00:00 EST 2000 · Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory

DOI:https://doi.org/10.1021/jp9928199· OSTI ID:20017298

Arnold, S T; Dotan, I; Williams, S; Viggiano, A A; Morris, R A

Rate constants and product branching fractions are reported for reactions of the air plasma cations NO{sup +}, O{sub 2}{sup +}, O{sup +}, N{sup +}, and N{sub 2}{sup +} with several alkylbenzenes: toluene, ethylbenzene, n-propylbenzene, and m-xylene. The measurements were made using a selected ion flow tube (SIFT) apparatus at 300 K. All reactions were found to proceed at the collision rate. NO{sup +} reactions yield exclusively nondissociative charge-transfer products. C{sub 7}H{sub 7}{sup +} is the dominant product ion observed in all the O{sup +}, N{sup +}, and N{sub 2}{sup +} reactions. Charge transfer and formation of C{sub 7}H{sub 7}{sup +} are the major product channels in the O{sub 2}{sup +} reactions. Product distributions were converted to crude breakdown diagrams, showing the relative abundance of each product ion as a function of the reactant ion recombination energy. The flow tube results exhibit a shift in the product ion threshold energies, an effect attributed to a kinetic shift resulting from slow fragmentation of the excited charge-transfer complex combined with collisional stabilization of the complex by the He buffer gas. Two isomeric forms of the C{sub 7}H{sub 7}{sup +} product ion are produced in these reactions: the benzyl (Bz{sup +}) and tropylium (Tr{sup +}) cations. The Bz{sup +}/Tr{sup +} isomeric mixture ratio was quantified as a function of energy for all four alkylbenzenes. Changes in the Bz{sup +}/Tr{sup +} mixture suggest that ethylbenzene has a relatively larger reverse activation barrier compared with toluene for forming Tr{sup +} from the charge-transfer complex, while formation of Tr{sup +} from the larger alkylbenzenes probably proceeds via a different mechanism altogether. For m-xylene, the formation of both Bz{sup +} and Tr{sup +} isomers likely proceeds via a different mechanism than for the n-alkylbenzenes.

• Research Organization: Air Force Research Lab., Hanscom AFB, MA (US)
• OSTI ID: 20017298
• Journal Information: Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory, Journal Name: Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory Journal Issue: 5 Vol. 104; ISSN 1089-5639; ISSN JPCAFH
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AIR
AIR POLLUTION CONTROL
ALKYLATED AROMATICS
NITROGEN
NITROGEN OXIDES
OXYGEN
TOLUENE
XYLENES