The Study of Cold Collisions Using Ion Guides and Traps

Gerlich, D.

doi:10.1142/9781848162105_0003

Cited by 42 publications

(36 citation statements)

References 48 publications

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“…The OPR of H 2 has a major impact on the key reaction initiating the nitrogen hydride synthesis in cold gas conditions, N + + H 2 → NH + + H, which possesses a small endoergicity of the order of the energy difference between the lowest rotational fundamental states of ortho-and para-H 2 (∼170 K, Gerlich 2008). A succession of hydrogenations of the NH + n ions (with n = 1−3) follows, leading to the formation of the ion ammonium (NH + 4 ).…”

Section: Deviation From Thermodynamical Equilibriummentioning

confidence: 99%

Ortho-to-para ratio of NH₂

Persson

Olofsson

Gal

et al. 2016

A&A

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We have used the Herschel-HIFI instrument to observe the two nuclear spin symmetries of amidogen (NH 2 ) towards the high-mass star-forming regions W31C (G10.6−0.4), W49N (G43.2−0.1), W51 (G49.5−0.4), and G34.3+0.1. The aim is to investigate the ratio of nuclear spin types, the ortho-to-para ratio (OPR) of NH 2 in the translucent interstellar gas, where it is traced by the line-of-sight absorption, and in the envelopes that surround the hot cores. The HIFI instrument allows spectrally resolved observations of NH 2 that show a complicated pattern of hyperfine structure components in all its rotational transitions. The excited NH 2 transitions were used to construct radiative transfer models of the hot cores and surrounding envelopes to investigate the excitation and possible emission of the ground-state rotational transitions of ortho-NH 2 N Ka,Kc J = 1 1,1 3/2-0 0,0 1/2 (953 GHz) and para-NH 2 2 1,2 5/2-1 0,1 3/2 (1444 GHz) used in the OPR calculations. Our best estimate of the average OPR in the envelopes lie above the high-temperature limit of three for W49N, specifically 3.5 with formal errors of ±0.1, but for W31C, W51, and G34.3+0.1 we find lower values of 2.5 ± 0.1, 2.7 ± 0.1, and 2.3 ± 0.1, respectively. Values this low are strictly forbidden in thermodynamical equilibrium since the OPR is expected to increase above three at low temperatures. In the translucent interstellar gas towards W31C, where the excitation effects are low, we find similar values between 2.2 ± 0.2 and 2.9 ± 0.2. In contrast, we find an OPR of 3.4 ± 0.1 in the dense and cold filament connected to W51 and also two lower limits of 4.2 and 5.0 in two other translucent gas components towards W31C and W49N. At low temperatures (T 50 K) the OPR of H 2 is <10 −1 , far lower than the terrestrial laboratory normal value of three. In this para-enriched H 2 gas, our astrochemical models can reproduce the variations of the observed OPR, both below and above the thermodynamical equilibrium value, by considering nuclear-spin gas-phase chemistry. The models suggest that values below three arise in regions with temperatures 20−25 K, depending on time, and values above three at lower temperatures.

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Section: Deviation From Thermodynamical Equilibriummentioning

confidence: 99%

Ortho-to-para ratio of NH₂

Persson

Olofsson

Gal

et al. 2016

A&A

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“…Only a limited number of these powerful tools, however, were able to deliver data at the lowest temperatures prevailing in the coldest environment of the interstellar medium. It is in the 1980s and early 1990s that several techniques were developed for the study of ion-molecule reactions down to temperatures close to 10 K [20,45].…”

Section: Ion-molecule Reactionsmentioning

confidence: 99%

“…However, in this technique the ions are not strictly equilibrated at the apparatus temperature and their velocity distribution is not Maxwell-Boltzmann because of the presence of electric fields [20]. This method, as well as the cryogenically cooled Penning trap experiment of Dunn and coworkers [48], has not been widely used and most of the developments of cryogenically cooled methods have been performed by Gerlich and co-workers using radiofrequency traps with special geometries to minimise heating of the ions due to radiofrequency fields [45,49]. It is worth mentioning a series of recent experiments on ion -H reactions using an innovative version of the apparatus [49,50].…”

Section: Ion-molecule Reactionsmentioning

confidence: 99%

“…∼10 K). With the molecular beam and ion guiding techniques available today, sub-meV (<10 K) collision energies are potentially achievable [45].…”

Section: Ion-molecule Reactionsmentioning

confidence: 99%

“…There is however a significant amount of data that were obtained at room temperature [104] for H, N and O atoms using the SIFT apparatus. The first attempt made by D. Gerlich, using an innovative ion trap, concerning the reactivity of H atoms at temperatures below 100 K is clearly promising [45,49] and could be extended to N, O or possibly metal atoms. This kind of studies could also be considered in the CRESU apparatus in Rennes provided that a stable and dense atom source is implemented.…”

Section: Charges Speciesmentioning

confidence: 99%

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Gas phase reactive collisions, experimental approach

Canosa

2011

EPJ Web of Conferences

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Abstract. Since 1937 when the first molecule in space has been identified, more than 150 molecules have been detected. Understanding the fate of these molecules requires having a perfect view of their photochemistry and reactivity with other partners. It is then crucial to identify the main processes that will produce and destroy them. In this chapter, a general view of experimental techniques able to deliver gas phase chemical kinetics data at low and very low temperatures will be presented. These techniques apply to the study of reactions between neutral reactants on the one hand and reactions involving charge species on the other hand.

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