Quantum State-Resolved Study of the Four-Atom Reaction OH^- (XΣ⁺) + D₂ (X¹Σ_g⁺, v = 0) → HOD (X¹A‘, v‘) + D^- (¹S)

Abstract

The D+ transfer reaction between OH- (X1sigma+) and D2 was studied with crossed molecular beam experiments and quantum chemical calculations at collision energies of 89 and 68 kJ/mol. The D- product ions were observed and measured for the first time in the crossed beam experiments. The center-of-mass (c.m.) flux distributions of the D- product ions exhibit significant asymmetry, and their maxima are close to the velocity and direction of the precursor D2 beam. The data are consistent with a direct mechanism that occurs on a time scale significantly less than a rotational period of the transient complex formed by approaching reactants. The D+ transfer results primarily in the excitation of the H-O-D bending vibrational mode of the molecular product. The experimental observation is in agreement with theoretical results showing that, during the D+ transfer, the H-O-D bond angle changes significantly.

H/D exchange in reactions of OH− with D2 and of OD− with H2 at low temperatures

“…Potential energy surfaces are available. 33,34,38 First hints to a possible orientation dependence during the approach of the reactants may be obtained from trajectory calculations. Trajectories, started somewhere in the three potential minima, may provide information on the efficiency of H/D scrambling.…”

“…36 A common way to probe reaction dynamics and to learn more about the H 3 O À collision complex is to use isotope labelling and to look for scrambling of the chemically equivalent atoms. In the following, we will discuss the two isotope exchange reactions, which have been studied experimentally before, [38][39][40][41][42]…”

On the dynamics of chemical reactions of negative ions

“…In the measured narrow angular distribution it was found that the reaction occurs fast on the time scale of rotation of the OH − (H 2 ) reaction complex. In a study of the proton transfer reaction channel, forming HOD + D − , also a very narrow velocity distribution was extracted [123]. The reconstructed velocity distribution in the scattering plane is reproduced in Fig.…”

“…In addition they could study inelastic scattering via the O − (H 2 O) reaction complex. More recently, non-reactive and reactive collisions of OH − anions with D 2 molecules have been studied by the same group [123,127]. In the isotopic exchange reaction channel, the formation of OD − + HD, no energy dependence was found between 0.27 and 0.69 eV relative collision energy [127].…”

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

“…The proton transfer and charge transfer products are clearly formed in large impact parameter collisions, suggesting that the centrifugal barrier associated with the long-range attractive potential of the approaching reactants prevents the reactants from reaching the short range part of the potential where C-O bond formation occurs. In previous works, 4,5,[23][24][25] we have shown that the electrostatic complexes that characterize reactions proceeding through large impact parameters decay with rates near 10 14 s −1 , further suggesting that processes that may occur via slow isomerization pathways will result in product levels below the detection limit.…”