Formation of complex organics from acetylene catalyzed by ionized benzene.

We present direct evidence for low temperature associative charge transfer (ACT) reactions of acetylene onto the benzene cation that catalyze the conversion of acetylene molecules into polymerized cations and for high temperature addition/elimination reactions that lead to the generation of naphthalene-type ions. At low temperatures acetylene molecules bind noncovalently to the benzene cation, where partial charge transfer from the ion activates an acetylene molecule for addition polymerization with other associated acetylene molecules, thus amounting to catalytic cyclization/polymerization of the acetylene molecules. At high temperatures the barrier of the covalent addition of acetylene to the benzene cation to form a styrene-type ion is measured as 3.5 kcal/mol. The second acetylene addition followed by H elimination to form a naphthalene-type ion is calculated to be highly exothermic and without a barrier. These reactions can explain the formation of complex organics by gas phase ion-molecule reactions under a wide range of temperatures and pressures in astrochemical environments.

Hydrogen bonding interactions of pyridine*+ with water: stepwise solvation of distonic cations.

The solvation energies of the pyridine*+ radical cation by 1-4 H2O molecules were determined by equilibrium measurements in a drift cell. The binding energies of the pyridine*+(H2O)n clusters are similar to the binding energies of protonated pyridine-water clusters, (C5H5NH+)(H2O)n, which involve NH+..OH2 bonds and different from those of the solvated benzene radical cation-water clusters, C6H6*+(H2O)n, which involve CHdelta+..OH2 bonds. These relations indicate that the observed pyridine*+ ions have the distonic *C5H4NH+ structures that can form NH+..OH2 bonds. The observed thermochemistry and ab initio calculations show that these bonds are not affected significantly by an unpaired electron at another site of the ion. Similar observations also identify the 2-fluoropyridine*+ distonic ion. The distonic structure is also consistent with the reactivity of pyridine*+ in H atom transfer, intra-cluster proton transfer and deprotonation reactions. The results present the first measured stepwise solvation energies of distonic ions, and demonstrate that cluster thermochemistry can identify distonic structures.

Reactions of CH3OCH2+ with hydrocarbons and O, N, and S compounds: applications for chemical ionization in selected ion flow tube studies.

We report the results of a flowing afterglow ion source-selected ion flow tube study (FA-SIFT) of the reactions of the methoxymethyl cation, CH3OCH2+. Rate coefficients and product branching ratios are reported for twenty nine reagent molecules including those that constitute the major ingredients of air, the hydrocarbons CH4, C2H6, C3H8, n-C4H10, C2H2, C2H4, C3H4 (allene and propyne), C6H6, and the S-containing molecules H2S, CH3SH, C2H5SH, (CH3)2SH, and (C2H5)2SH. In addition, we examined the reactions with the N-containing molecules NH3, CH3NH2, (CH3)2NH, (CH3)3N, pyrrole, pyridine as well as CH3COCH3. The results can be summarized under three general reaction types: Reaction at the CH3 carbon, reaction at the CH2 carbon, and association. The results also indicate that the methoxymethyl cation can be used as a chemical ionization source for the detection of trace levels of S-containing compounds in saturated hydrocarbons.