Reactivity of C2H5+ with Benzene: Formation of Ethylbenzenium Ions and Implications for Titan’s Ionospheric Chemistry

Abstract

The reaction of ethyl cation with benzene has been investigated in a combined experimental and theoretical approach. Under single collision conditions, proton transfer affording protonated benzene concomitant with neutral ethene represents the major reaction channel. From pressure-dependent measurements, an absolute cross section of 7 +/- 2 A(2) at hyperthermal energies (about 1.0 eV in the center of mass frame) is derived for this channel, from which a phenomenological rate constant of about 2.9 x 10(-10) cm(3) s(-1) is estimated at low energies. The energy behavior of the cross section as well as several side reactions leading to C-C coupling imply that the reaction of C(2)H(5)(+) with C(6)H(6) proceeds via a long-lived association product, presumably the covalently bound protonated ethylbenzene (ethylbenzenium ion). With regard to chemical processes in the atmosphere of Titan, present results imply that termolecular association of C(2)H(5)(+) with benzene to produce protonated ethylbenzene is very likely to occur. The condensation of alkyl cations with arenes thus provides an alternative route for the growth of larger hydrocarbon molecules.