Recombination of H3+ Ions in the Afterglow of a He-Ar-H2 Plasma

TL;DR

This study investigates the recombination processes of H3+ ions in a helium-based low-temperature plasma, identifying key rate coefficients and proposing a mechanism involving Rydberg neutral H3 formation and collisions with helium.

Contribution

It provides experimental rate coefficients for H3+ recombination in helium plasma and proposes a detailed mechanism involving Rydberg states and helium collisions.

Findings

Two-body recombination rate matches previous experiments and theory.

Three-body recombination involves formation of excited Rydberg H3 and helium collisions.

Presence of H3 confirmed by plasma electron spectroscopy.

Abstract

Recombination of H3+ with electrons was studied in a low temperature plasma in helium. The plasma recombination rate is driven by two body, H3+ + e, and three-body, H3+ + e + He, processes with the rate coefficients 7.5x10^{-8}cm3/s and 2.8x10^{-25}cm6/s correspondingly at 260K. 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.