Mutual neutralization of H ₃ ⁺ and H ⁻ ions in slow collisions

Abstract

The process of mutual neutralization of H3+ and H− ions in the CM collision energy range 0.1 eV/u–10 keV/u is studied within the multi-channel Landau-Zener model. From the multitude of covalent H3* + H(1s) states only the states (2s)2A′1, (3s)2A′1 and (3d)2A′1 are strongly coupled with the initial ionic H3+ +H− state. The total mutual-neutralization cross-section has a broad maximum around ECM = 1 keV/u of about 3 × 10−15 cm2, and below ∼ 100 eV/u it monotonically increases with decreasing the collision energy, surpassing a value of ∼ 3 × 10−13 cm2 below ECM = 0.1 eV/u. The mutual neutralization of H3+ and H− ions is, therefore, an important process in cold hydrogen plasmas.

Global model analysis of negative ion generation in low-pressure inductively coupled hydrogen plasmas with bi-Maxwellian electron energy distributions

“…33,51,52 Furthermore, the H þ 3 -H À mutual neutralization has the complexity that correlates with the predissociation channels of H 3 (produced by the electron capture in the collision of H þ 3 and H À ) to 3 H and H 2 þ H. Not only the total cross section of the H þ 3 -H À mutual neutralization, but also the predissociation branching ratio which is dependent on the H 3 excited states must be considered in principle. 53,54 For simplicity, the data from Eerden et al 50 was chosen as the cross sections of the H þ 2 -H À and H þ 3 -H À mutual neutralizations in the model, with consideration for the values reported by other references. [51][52][53][54] No cross section data were available for the vibrationtranslation energy transfer relaxation (or de-excitation) processes of the H-H 2 and H 2 -H 2 collisions, thus the temperature-dependent formulae of their rate constants (for the most dominant Dv ¼ 1 case) given by Mandy and Martin, 56 and Matveyev and Silakov 57 were employed, respectively.…”

“…53,54 For simplicity, the data from Eerden et al 50 was chosen as the cross sections of the H þ 2 -H À and H þ 3 -H À mutual neutralizations in the model, with consideration for the values reported by other references. [51][52][53][54] No cross section data were available for the vibrationtranslation energy transfer relaxation (or de-excitation) processes of the H-H 2 and H 2 -H 2 collisions, thus the temperature-dependent formulae of their rate constants (for the most dominant Dv ¼ 1 case) given by Mandy and Martin, 56 and Matveyev and Silakov 57 were employed, respectively. The H-H 2 vibration-translation energy transfer rate constants were calculated treating the effective gas temperature of H and H 2 as the temperature in the formula, as suggested by Biel et al 55 …”

Physics basis and future trends for negative ion sources (invited)

“…Recently Janev et al 12 performed a theoretical calculation of this cross section which is found to be five times lower than that obtained from Hickman's scaling. Figure 2 …”

Formation ofH3−by radiative association ofH2

“…We take the value of k ± ∼ 10 −7 cm 3 /s for the H − +H + →H+H reaction [36][37][38] at 10 meV. Therefore, we derive the equilibrium abundance of H − : n(H − ) = ζn(H 2 )f DA /(k ± n + ) ∼ 5 × 10 −7 cm −7 .…”