Announcement of the winner of the Longuet-Higgins Early Career Researcher Prize 2021

ABSTRACT The reactions between ground state and forming and were investigated in the range of collision energies between and 10 K using a merged-beam approach. The reaction rates measured experimentally are compared to those obtained for the reaction between and forming under similar experimental conditions. Below 1 K, a clear enhancement of the reaction rate coefficient compared to the Langevin rate measured at higher collision energies was observed in both reaction systems. This enhancement is interpreted as originating from the interaction between the charge of and the quadrupole of para and ortho molecules in the J = 1 rotational level. The enhancement of the reaction with was found to be significantly less than that of the reaction with , reflecting the relative population of the J = 1 rotational level of (75%) and (33%) in natural samples at low temperatures. Simulations of the experimental results based on the theoretical predictions of the reaction cross sections by Dashevskaya et al. [J. Chem. Phys. 145, 244315 (2016)] reveal agreement within the experimental uncertainties. The branching ratio η of the reaction involving and and forming and near E coll = 0 was determined to be 0.341(15). Time-of-flight measurements of the velocity distributions of the reaction products are compatible with an isotropic product emission with an average total kinetic energy of 0.45(5) eV for both channels, representing about 30% of the total energy released by the reaction. GRAPHICAL ABSTRACT