Deviation of the rate of thereaction from Langevin behaviour below 1 K, branching ratios for theandproduct channels, and product-kinetic-energy distributions

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Deviation of the rate of the reaction from Langevin behaviour below 1 K, branching ratios for the and product channels, and product-kinetic-energy distributions

Katharina Höveler, Johannes Deiglmayr, Frédéric Merkt

The reactions between ground-state

H2+

(X

2Σg+(v=0,J=0)

) and

D2

forming

HD2++H

and

H2D++D

were investigated in the range of collision energies

Ecoll

between

Ecoll/kB=0

and 10 K using a merged-beam approach. The reaction rates measured experimentally are compared to those obtained for the reaction between

H2+

and

H2

forming

H3++H

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

H2+

and the quadrupole of para

D2

and ortho

H2

molecules in the J = 1 rotational level. The enhancement of the reaction with

D2

was found to be significantly less than that of the reaction with

H2

, reflecting the relative population of the J = 1 rotational level of

H2

(75%) and

D2

(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

H2+

and

D2

and forming

H2D+

and D (

η=[H2D+][H2D+]+[HD2+]

) near

Ecoll=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

Publisher URL: https://www.tandfonline.com/doi/full/10.1080/00268976.2021.1954708

DOI: 10.1080/00268976.2021.1954708