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