Reaction dynamics of OH+(Σ−3)+C2H2 studied with crossed beams and density functional theory calculations

Abstract

The reactions between OH+(3Sigma-) and C2H2 have been studied using crossed ion and molecular beams and density functional theory calculations. Both charge transfer and proton transfer channels are observed. Products formed by carbon-carbon bond cleavage analogous to those formed in the isoelectronic O(3P)+C2H2 reaction, e.g., 3CH2 + HCO+, are not observed. The center of mass flux distributions of both product ions at three different energies are highly asymmetric, with maxima close to the velocity and direction of the precursor acetylene beam, characteristic of direct reactions. The internal energy distributions of the charge transfer products are independent of collision energy and are peaked at the reaction exothermicity, inconsistent with either the existence of favorable Franck-Condon factors or energy resonance. In proton transfer, almost the entire reaction exothermicity is transformed into product internal excitation, consistent with mixed energy release in which the proton is transferred with both the breaking and forming bonds extended. Most of the incremental translational energy in the two higher-energy experiments appears in product translational energy, providing an example of induced repulsive energy release.

Imaging the dynamics of ion–molecule reactions

“…In many of the systems investigated by Farrar and co-workers, charge transfer is dominant over proton transfer. Through a variation of the charge state (OH +/À + C 2 H 2 ) 69,70 or the proton donor (H 2 O + /H 3 O + + NH 3 ), 71,72 they were able to investigate the proton transfer dynamics. A direct stripping mechanism was found to be the only reaction pathway.…”