Recombination of H⁺₃ions in the afterglow of a He–Ar–H₂plasma

Abstract

Recombination of H + 3 with electrons was studied in a low temperature plasma in helium. The plasma recombination rate is driven by two body, H + 3 + e − , and three-body, H + 3 + e − + He, processes with the rate coefficients 7.5 × 10 −8 cm 3 s −1 and 2.8 × 10 −25 cm 6 s −1 correspondingly at 260 K. The two-body rate coefficient is in excellent agreement with results from storage ring experiments and theoretical calculations. We suggest that the three-body recombination involves formation of highly excited Rydberg neutral H3 followed by an l-or m-changing collision with He. Plasma electron spectroscopy indicates the presence of H3.

Binary recombination of para- and ortho-H 3 + with electrons at low temperatures

“…A similar approach was used in our recent study of binary recombination of para-H + 3 and ortho-H + 3 ions at temperatures close to 77 K [20]. In the present studies, we have extended the range of temperatures up to 200 K. Our previous measurements in H + 3 -and D + 3 -dominated plasmas at conditions similar to those in the present experiment [4,14,15,21,22] have shown that the H + 3 ions recombine by both a binary process with a rate coefficient a bin , and a ternary helium-assisted recombination mechanism, with a rate coefficient K He . The plasma decay can then be described by an overall effective recombination rate coefficient:…”

“…This resulted in a convergence with experimental DR data reported from ion storage rings where experimentalists had realized the impact of rotational excitation of the H + 3 ions on the DR reaction rate, especially with respect to the importance of the DR process in interstellar molecular clouds [11][12][13]. Final convergence between theory and the remaining important experimental techniques, stationary and flowing afterglow, was reached after recognizing that a fast third-body reaction, not previously considered, stabilizes the recombination process in such plasmas [4,14,15]. However, recently it has been shown [16,17] that the assumption of rotationally cold H + 3 ions in storage rings was not entirely correct [17].…”

State selective study of H3+recombination in Cryo-FALP and SA-CRDS experiments at 77 K

“…Measured ternary recombination rate coefficients also showed pronounced nuclear spin specificity at temperatures 100-200 K. Theory of the aforementioned ternary processes is based on a calculation of the life time of rotationaly excited neutral p/o H 3 Rydberg molecule. This molecule is formed in collision of p/o H + 3 with electron [18][19][20] and theory predicts the order of magnitude of the ternary rate coefficient correctly. However, the theory is not detailed enough for closer comparison with the experimental values of state selected ternary rate coefficients and their temperature dependencies.…”

“…[14][15][16][17] and references therein. In studies of binary recombination of H + 3 ions in He/Ar/H 2 gas mixture it was observed that the decay of afterglow plasma is dependent on He number density [5,6,[18][19][20]. This indicates that a ternary He-assisted recombination process contributes to the overall recombination in afterglow plasma in He/Ar/H 2 gas mixture:…”

Mid-IR laser action in the H3 Rydberg molecule and some possible astrophysical implications

“…Moreover, these d-to p-state transitions occur exactly in the region where lasing is observed, as shown in Figue 1. The flowing afterglow experiments of Glosik et al [6] suggest a 3-body "collision assisted recombination" mechanism, rather than a simple 2-body recombination process, because of the relatively high(> 10 14 cm-3) gas density obtaining in the supersonic discharge source. The Berkeley spectrometer used to produce and measure IR laser transitions generated in supersonic plasmas is described in Reference 3.…”