Observation of quantum capture in an ion-molecule reaction

Abstract

In 1954, Vogt and Wannier (Phys. Rev. 95, 1190) predicted that the capture rate of a polarizable neutral atom or molecule by an ion should increase by a factor of two compared to the classical Langevin rate as the collision energy approaches zero. This prediction has not been verified experimentally. The H${}_2^{+}$ + H${}_2$ reaction is ideally suited to observe this effect, because the small reduced mass makes quantum effects related to s-wave scattering observable at higher collision energies than in other systems. Moreover, the reaction rate for this barrierless, strongly exothermic reaction follows the classical Langevin capture model down to cold-collision conditions (about $k_{\mathrm{B}}\cdot 1\mathrm{K}$) and is not affected by short-range interactions. Below this temperature, a strong enhancement of the reaction rate resulting from charge--quadrupole interaction between H${}_2^{+}$ and ground-state ortho H${}_2$ ($J=1$) was observed. Here we present an experimental study of the reaction of H${}_2^{+}$ and para H${}_2$ ($J=0$), which has no dipole and no quadrupole moments, at collision energies below $k_{\mathrm{B}}\cdot 1\mathrm{K}$. We observe an enhancement at the lowest collision energies which is attributed to the quantum enhancement predicted by Vogt and Wannier. Measurements of the reaction of HD${}^{+}$ with HD support this conclusion.

8 pages, 6 figures

References in corpus (5)

• A trapped single ion inside a Bose-Einstein condensate
• Observation of enhanced rate coefficients in the H${}_2^{+}$ + H${}_2$ $\to$ H${}_3^{+}$ + H reaction at low collision energies
• Reactive collisions of trapped anions with ultracold atoms
• Ion-molecule reactions below 1~K: Observation of a strong enhancement of the reaction rate of the ion-dipole reaction He${}^{+}$+ CH${}_3$F
• Multipole-moment effects in ion-molecule reactions at low temperatures: part I -- Ion-dipole enhancement of the rate coefficients of the He${}^{+}$ + NH${}_3$ and He${}^{+}$ + ND${}_3$ reactions at collision energies near $0$ K

Cited by in corpus (1)

• Electrostatic trapping of N${}_2$ molecules in high Rydberg states