Flowing afterglow studies of the electron recombination of protonated cyanides (RCN)H+ and their proton-bound dimer ions (RCN)2H+ where R is H, CH3, and CH3CH2

A study has been made of the electron-ion dissociative recombination of the protonated cyanides (RCNH+, R = H, CH3, C2H5) and their proton-bound dimers (RCN)(2)H+ at 300 K. This has been accomplished with the flowing afterglow technique using an electrostatic Langmuir probe to determine the electron density decay along the flow tube. For the protonated species, the recombination coefficients, alpha(e)(cm(3) s(-1)), are (3.6 +/- 0.5) x 10(-7), (3.4 +/- 0.5) x 10(-7). (4.6 +/- 0.7) x 10(-7) for R = H, CH3, C2H5, respectively. For the proton-bound dimers, the alpha(e) are substantially greater being (2.4 +/- 0.4) x 10(-6), (2.8 +/- 0.4) x 10(-6), (2.3 +/- 0.3) x 10(-6) for R = H, CH3, C2H5, respectively. Fitting of the electron density decay data to a simple model has shown that the rate coefficients for the three-body association of RCNH+ with RCN are very large being (2.0 +/- 0.5) x 10(-26), cm(6) s(-1). The significance of these data to the Titan ionosphere is discussed. Published by Elsevier B.V.