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.

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We have investigated dissociative recombination (DR) of NH + with electrons using a merged beams configuration at the TSR heavy-ion storage ring located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We present our measured absolute merged beams recombination rate coefficient for collision energies from 0 to 12 eV. From these data we have extracted a cross section which we have transformed to a plasma rate coefficient for the collisional plasma temperature range from T pl = 10 to 18000 K. We show that the NH + DR rate coefficient data in current astrochemical models are underestimated by up to a factor of ∼ 9. Our new data will result in predicted NH + abundances lower than calculated by present models. This is in agreement with the sensitivity limits of all observations attempting to detect NH + in interstellar clouds.In the cold ISM, such as in molecular clouds, the most abundant nitrogen-bearing species are expected to be N and N 2 (Langer & Graedel 1989). However, direct observation of these is difficult. Atomic N does not have any low-lying, fine-structure levels that can be populated at molecular cloud temperatures and N 2 lacks a dipole moment, which is needed to provide reasonably strong ro-vibrational transitions. Thus, observations of tracers such as NH, NH 2 , NH 3 , or N 2 H + must be used to infer the N and N 2 abundances through chemical models.Neutral nitrogen hydrides are widely seen in the ISM. Ammonia (NH 3 ) was first detected by Cheung et al. (1968). Later NH 2 and NH were identified by van Dishoeck et al. (1993) and Meyer & Roth (1991), respectively. The observed abundances, however, do not match predictions from astrochemical models. In diffuse interstellar clouds, observed abundance ratio for NH/NH 3 are ∼ 1.7 and for NH 3 /H ∼ 3.2 × 10 −9 . These cannot be simultaneously explained by existing chemical models. The models can fit either one of the observed values but then the other predicted ratio is a factor of 10 off from the observation (Persson et al. 2010). Similarly, in dark clouds the abundance ratio for NH/NH 3 is underpredicted by more than an order of magnitude (Hily-Blant et al. 2010). These discrepancies possibly originate from using incorrect reaction rate coefficients in the models.

0953-4075/14/035201+06$33.00