Observation of quantum capture in an ion-molecule reaction

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