Formation and recombination of protonated acetonitrile clusters

Formation of the protonated acetonitrile cluster ions CH3CNH+. CH3CN and their subsequent dissociative recombination with electrons was studied in a high-pressure flowing afterglow using the axially movable Langmuir probe. The first step is the binary proton transfer reaction of H3O+ with CH3CN With the rate coefficient k(1) = (5.9 +/- 1.9) x 10(-9) cm(3) s(-1). Resulting CH3CNH+ ions further associate with the neutral acetonitrile molecules at pressures 3-5 Ton with the effective binary rate coefficient k(2eff) = (2.1 +/- 0.7) x 10(-9) cm(3) s(-1) forming the clusters H+.(CH3CN)(2). Further reaction of these clusters with CH3CN is very slow with the effective binary rate coefficient k(3eff) = (1.1 +/- 0.3) x 10(-12) cm(3) s(-1). The large difference between k(2eff) and k(3eff) facilitated the study of dissociative recombination of H+.(CH3CN)(2) cluster ions with electrons at thermal energy and pressure p = 4.5-7.0 Torr. The recombination rate coefficient thus obtained is (2.8 +/- 1) x 10(-6) cm(3) s(-1).