2025 Articles

Controlling the internal excitation of H₃⁺ produced in a duoplasmatron ion source

Ivanov, Dmitry; Bu, Caixia; P.-M. Hillenbrand,; D. Schury,; Urbain, Xavier; Savin, Daniel Wolf

We have explored a combination of two methods to control the internal excitation of H₃⁺ produced in a duoplasmatron ion source. The H₃⁺ was formed starting from a gas of H₂. The first control method varied the H₂ pressure in the ion source to collisionally relax any internally excited (H₃⁺) ∗. The second method added Ar to the source to chemically destroy (H₃⁺) ∗ with internal excitation energies Eint ⩾ 0.57 eV, using the endoergic reaction H₃⁺ + Ar → ArH+ + H₂. To infer the H₃⁺ internal temperature, Tᵢₙₜ, representative of internal excitation under the hypothesis of thermodynamic equilibrium, we used merged-beams rate coefficient measurements of the endoergic deuterating reaction H₃⁺ + D → H₂D⁺ + H₂ and a semi-empirical theoretical model. We found that using collisional relaxation alone, we could vary Tᵢₙₜ over the range ≈1300 − 2200 K. Combining collisional relaxation and chemical destruction, we reduced the minimum to Tᵢₙₜ ≈ 1130 K. Over this temperature range, the fraction of H₃⁺ where all vibrational modes are in their v = 0 level varies from ≈0.88 at the lowest temperature to ≈0.44 at the highest temperature. This combination of cooling methods offers a potentially powerful means for studying reactive scattering processes as a function of the internal excitation of the H₃⁺.