High-resolution storage-ring measurements of the dissociative recombination ofH3+using a supersonic expansion ion source

Abstract

We have performed measurements of the dissociative electron recombination (DR) of H + 3 at the ion storage ring TSR utilizing a supersonic expansion ion source. The ion source has been characterized by continuous wave cavity ring-down spectroscopy. We present high-resolution DR rate coefficients for different nuclear spin modifications of H + 3 combined with precise fragment imaging studies of the internal excitation of the H + 3 ions inside the storage ring. The measurements resolve changes in the energy dependence between the ortho-H + 3 and para-H + 3 rate coefficients at low center-of-mass collision energies. Analysis of the imaging data indicates that the stored H + 3 ions may have higher rotational temperatures than previously assumed, most likely due to collisional heating during the extraction of the ions from the ion source. Simulations of the ion extraction shed light on possible origins of the heating process and how to avoid it in future experiments.

Chemistry, astronomy and physics of H 3 +

“…(ii) The large difference of DR rates for ortho-and para-H + 3 predicted by the theory is not observed experimentally [22,24,30]. For the latter, Glosik's group has published papers that agree better with theoretical predictions [31,32].…”

“…Both discrepancies among experimental values of the DR rate constants, and those between experiment and theory, have been greatly reduced. The advent of a low-temperature ion source has led to a nearperfect agreement between the experiments by both the CRYRING [20] and the TSR on the energy-dependent resonant structure [21] and the cross section [22].…”

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

“…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]. This is important if we realize that the quantum mechanical calculations [18] predict a large difference in the low-temperature recombination of ions in para-H + 3 and ortho-H + 3 states.…”

Production of a rovibrationally selected O2+beam for dissociative recombination studies

“…In all cases, the proper selection of low angular momentum states will require the parent O 2 gas to be cooled by supersonic expansion, which raises the issue of unwanted collisions in the acceleration process, that may alter the selectivity of the REMPI technique. Such an effect has been discussed by Kreckel et al [12] for H + 3 . The implementation of a laser ion source is foreseen for DR measurements at the CSR storage ring in Heidelberg, for direct injection of cold or selected ions of infrared inactive species.…”