High-resolution storage-ring measurements of the dissociative recombination of H3+ using a supersonic expansion ion source

We have performed measurements of the dissociative electron recombination (DR) of H3+ 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 H3+ combined with precise fragment imaging studies of the internal excitation of the H3+ ions inside the storage ring. The measurements resolve changes in the energy dependence between the ortho-H3+ and para-H3+ rate coefficients at low center-of-mass collision energies. Analysis of the imaging data indicates that the stored H3+ 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.