The H₂⁺ + HD reaction at low collision energies: H₃⁺/H₂D⁺ branching ratio and product-kinetic-energy distributions

Abstract

The reactions between H2+ and HD forming H3+ + D as well as H2D+ + H were measured at collision energies between 0 and kB·30 K and a resolution of 75 mK and the H3+/H2D+ product branching ratio and the product kinetic-energy distribution were determined.

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

“…Several modifications introduced to improve the collision-energy resolution, the sensitivity of the product-ion detection, and the stability of the optical and mechanical components are described in Ref. [45], which also explains in detail, with the example of the reaction between H + 2 and HD forming H + 3 + D and H 2 D + + H, how the kinetic-energy distributions of the products and the branching ratios between different reaction channels are measured. We present here only the main aspects of 2 + H 2 and H + 2 + D 2 reactions at low collision energies, with (i) the source chambers containing pulsed valves emitting supersonic beams of either H 2 or D 2 (D 2 source chamber) and H 2 (H 2 source chamber), (ii) the deflection and reaction chamber containing the photoexcitation zone, where H 2 molecules are photoexcited to Rydberg-Stark states, the Rydberg-Stark deflector and decelerator used to merge the two beams, and the electrode stack surrounding the reaction zone used to extract the product ions, and (iii) the detection chamber where the product-ion yields are monitored using an MCP detector.…”

“…the measurements and the aspects that are specific to the H + 2 + D 2 reaction system and refer to articles [43,45] for further details.…”

“…The Rydberg electron shields the reaction system from heating effects by stray electric fields. Moreover, the large dipole moments of Rydberg states enable the control of the motion of Rydberg atoms and molecules using Rydberg-Stark decelerators and deflectors [36][37][38][39][40][41], opening access to studies of ion-molecule reactions at very low collision energies in merged beams [42][43][44][45]. Recent studies based on this approach revealed pronounced enhancements of the reaction rate coefficients below 1 K in capture reactions resulting from the iondipole interaction in the He + + CH 3 F reaction [44] and from the ion-quadrupole interaction in the H + 2 + H 2 [42] reaction, but not in the H + 2 + HD [45] reaction.…”

“…Moreover, the large dipole moments of Rydberg states enable the control of the motion of Rydberg atoms and molecules using Rydberg-Stark decelerators and deflectors [36][37][38][39][40][41], opening access to studies of ion-molecule reactions at very low collision energies in merged beams [42][43][44][45]. Recent studies based on this approach revealed pronounced enhancements of the reaction rate coefficients below 1 K in capture reactions resulting from the iondipole interaction in the He + + CH 3 F reaction [44] and from the ion-quadrupole interaction in the H + 2 + H 2 [42] reaction, but not in the H + 2 + HD [45] reaction. In this article, we report on the study of the ionquadrupole interaction in the reaction between H + 2 and D 2 forming H 2 D + + D and HD + 2 + H and on the quantitative comparison of the collision-energy dependence of the reaction rate coefficient with that of the H + 2 + H 2 reaction forming H +…”

Roadmap on dynamics of molecules and clusters in the gas phase

“…The ultralow energies are reached by merging a supersonic beam of the neutral in its ground state with a second supersonic beam of the Rydberg atom or molecule translationally cooled using a surface-electrode Rydberg-Stark decelerator and deflector. The technique has been used so far to investigate the reaction of He + with CH 3 F and, more recently, of H + 2 with HD [101]. The second breakthrough is the possibility to generate cold molecular ions by sympathetic cooling of charged species with laser-cooled atomic ions in Coulomb crystals.…”