Temperature dependence of binary and ternary recombination of H3+ ions with electron

We study binary and the recently discovered process of ternary He-assisted recombination of H3+ ions with electrons in a low temperature afterglow plasma. The experiments are carried out over a broad range of pressures and temperatures of an afterglow plasma in a helium buffer gas. Binary and He-assisted ternary recombination are observed and the corresponding recombination rate coefficients are extracted for temperatures from 77 K to 330 K. We describe the observed ternary recombination as a two-step mechanism: First, a rotationally-excited long-lived neutral molecule H3* is formed in electron-H3+ collisions. Second, the H3* molecule collides with a helium atom that leads to the formation of a very long-lived Rydberg state with high orbital momentum. We present calculations of the lifetimes of H3* and of the ternary recombination rate coefficients for para and ortho-H3+. The calculations show a large difference between the ternary recombination rate coefficients of ortho- and para-H3+ at temperatures below 300 K. The measured binary and ternary rate coefficients are in reasonable agreement with the calculated values.Comment: 15 page

Temperature dependence of binary and ternary recombination of D-3(+) ions with electrons

Flowing and stationary afterglow experiments were performed to study the recombination of D-3(+) ions with electrons at temperatures from 77 to 300 K. A linear dependence of apparent (effective) binary recombination rate coefficients on the pressure of the helium buffer gas was observed. Binary (D-3(+)+e(-)) and ternary (D-3(+)+e(-)+He) recombination rate coefficients were derived. The obtained binary rate coefficient agrees with recent theoretical values for dissociative recombination of D-3(+). We describe the observed ternary process by a mechanism with two rate determining steps. In the first step, a rotationally excited long-lived neutral D-3* is formed in D-3(+)-e(-) collisions. As the second step, the D-3* collides with a helium atom that prevents autoionization of D-3*. We calculate lifetimes of D-3* formed from ortho-, para-, or metastates of D-3(+) and use the lifetimes to calculate ternary recombination rate coefficients

Binary And Ternary Recombination Of H3\u3csup\u3e+\u3c/sup\u3e And D 3\u3csup\u3e+\u3c/sup\u3e Ions With Electrons In Low Temperature Plasma

Measurements of recombination rate coefficients of binary and ternary recombination of H3+ and D3+ ions with electrons in a low temperature plasma are described. The experiments were carried out in the afterglow plasma in helium with a small admixture of Ar and parent gas (H2 or D2). For both ions a linear increase of measured apparent binary recombination rate coefficients (αeff) with increasing helium density was observed: αeff = αBIN + KHe[He]. From the measured dependencies, we have obtained for both ions the binary (αBIN) and the ternary (KHe) rate coefficients and their temperature dependence. For the description of observed ternary recombination a mechanism with two subsequent rate determining steps is proposed. In the first step, in H3++ e- (or D3++ e-) collision, a rotationally excited long-lived Rydberg molecule H3* (or D 3*) is formed. In the following step H 3* (or D3*) collides with a He atom of the buffer gas and this collision prevents autoionization of H3* (or D3*). Lifetimes of the formed H3* (or D3*) and corresponding ternary recombination rate coefficients have been calculated. The theoretical and measured binary and ternary recombination rate coefficients obtained for H3+ and D3+ ions are in good agreement. © 2010 Taylor & Francis

8. Symposium on Application of Plasma Processes Study of Astrophysically Relevant Hydrogen Chemistry: combining an RF Ion Trap with a Cold Effusive Beam

Abstract This contribution presents recent progress made with an ion trapping instrument which is operated in the Department of Surface and Plasma Physics of Charles University. A special feature of the experimental setup is the combination of a low temperature 22-pole trap (22PT) with a cold effusive source for neutrals. This allows us to study the interaction of trapped ions with slow and cold neutrals. Using a discharge tube also radicals can be produced, especially H-or D-atoms. Recent experimental progress includes the extension of the temperature of the neutrals, T ACC , down to 4 K and various improvements on the accommodator for getting stable dissociation degrees. Using an MCP detector, the chemistry of both cations and anions can be studied. The instrument is presently used to explore a variety of pure hydrogen reactions at low temperatures. As a typical result, the formation of H 3 + via radiative and ternary association of H + an H 2 at 10 K will be discussed as well as the following formation of small hydrogen clusters. The conclusion and outlook give some hints to planned activities such as determination of state specific rate coefficients, the role of nuclear spin, and deuteration