Observation of enhanced rate coefficients in the H$_2^+$ + H$_2$ $\rightarrow$ H$_3^+$ + H reaction at low collision energies

TL;DR

This study measures the reaction rate of H$_2^+$ with H$_2$ at very low energies, revealing enhanced rates below 1 K due to quantum effects, and confirms recent theoretical predictions.

Contribution

First experimental measurement of the H$_2^+$ + H$_2$ reaction rate at low collision energies, demonstrating deviations from classical models and validating recent quantum predictions.

Findings

Rate coefficient deviates from classical behavior below 1 K

Enhanced reaction rates due to ion-quadrupole and Coriolis interactions

Experimental results agree with recent theoretical predictions

Abstract

The energy dependence of the rate coefficient of the H$_2^+\ + {\rm H}_2 \rightarrow {\rm H}_3^+ + {\rm H}$ reaction has been measured in the range of collision energies between $k_\mathrm{B}\cdot 10$ K and $k_\mathrm{B}\cdot 300$ mK. A clear deviation of the rate coefficient from the value expected on the basis of the classical Langevin-capture behavior has been observed at collision energies below $k_\mathrm{B}\cdot 1$ K, which is attributed to the joint effects of the ion-quadrupole and Coriolis interactions in collisions involving ortho-H$_2$ molecules in the $j = 1$ rotational level, which make up 75% of the population of the neutral H$_2$ molecules in the experiments. The experimental results are compared to very recent predictions by Dashevskaya, Litvin, Nikitin and Troe (J. Chem. Phys., in press), with which they are in agreement.