We have performed chemical probing spectroscopy of H + 3 ions trapped in a cryogenic 22-pole ion trap. The ions were buffer-gas cooled to ∼ 55 K by collisions with helium and argon. Excitation to states above the barrier to linearity was achieved by a Ti:Sa laser operated between 11 300 and 13 300 cm −1 . Subsequent collisions of the excited H + 3 ions with argon lead to the formation of ArH + ions that were detected by a quadrupole mass spectrometer with high sensitivity. We report the observation of 17 previously unobserved transitions to states above the barrier to linearity.Comparison to theoretical calculations suggests that the transition strengths of some of these lines are more than five orders of magnitude smaller than those of the fundamental band, which renders them -to the best of our knowledge -the weakest H + 3 transitions observed to date.

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.

We present the concluding result from an Ives-Stilwell-type time dilation experiment using 7Li+ ions confined at a velocity of β=v/c=0.338 in the storage ring ESR at Darmstadt. A Λ-type three-level system within the hyperfine structure of the 7Li+3S1 →3P2 line is driven by two laser beams aligned parallel and antiparallel relative to the ion beam. The lasers' Doppler shifted frequencies required for resonance are measured with an accuracy of <4×10(-9) using optical-optical double resonance spectroscopy. This allows us to verify the special relativity relation between the time dilation factor γ and the velocity β, γ√1-β2=1 to within ±2.3×10(-9) at this velocity. The result, which is singled out by a high boost velocity β, is also interpreted within Lorentz invariance violating test theories.

High-resolution dissociative recombination rate coefficients of rotationally cool and hot H 3 + in the vibrational ground state have been measured with a 22-pole trap setup and a Penning ion source, respectively, at the ion storage-ring TSR. The experimental results are compared with theoretical calculations to explore the dependence of the rate coefficient on ion temperature and to study the contributions of different symmetries to probe the rich predicted resonance spectrum. The kinetic energy release was investigated by fragment imaging to derive internal temperatures of the stored parent ions under differing experimental conditions. A systematic experimental assessment of heating effects is performed which, together with a survey of other recent storage-ring data, suggests that the present rotationally cool rate-coefficient measurement was performed at 380 +50 −130 K and that this is the lowest rotational temperature so far realized in storage-ring rate-coefficient measurements on H 3 + . This partially supports the theoretical suggestion that temperatures higher than assumed in earlier experiments are the main cause for the large gap between the experimental and the theoretical rate coefficients. For the rotationally hot rate-coefficient measurement a temperature of below 3250 K is derived. From these higher-temperature results it is found that increasing the rotational ion temperature in the calculations cannot fully close the gap between the theoretical and the experimental rate coefficients.

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