Effect of rotational excitation of H₂ on isotopic exchange reaction with OD⁻ at low temperatures

Abstract

Aims. This paper presents experimentally obtained rate coefficients for the weakly endothermic reaction OD − + H 2 → OH − + HD with ortho-and para-hydrogen at astrophysically relevant temperatures between 10 and 300 K. Methods. The reaction was studied with normal and para-enriched (99.5% para-H 2 ) hydrogen in a 22-pole ion trap. The measured temperature dependencies of reaction rate coefficients are analyzed using a model which assumes that the rotational energies of the two reactants are equivalent to the translational energy in driving the reaction. Results. At room temperature, the rate coefficients of reactions with both nuclear spin variants reach 7 × 10 −11 cm 3 s −1 , which is in good agreement with the previous results from ion trap and swarm experiments with normal hydrogen. Cooling down the trap slows down the reaction and leads, at a nominal trap temperature of 11 K, to a rate coefficient below 10 −14 cm 3 s −1 for paraenriched hydrogen. The fitted reaction endothermicity of 25.3 ± 2.2 meV agrees well with the literature value calculated in the Born-Oppenheimer approximation, ∆H 0 = 24.0 meV. A simpler evaluation procedure, fitting the data with Arrhenius functions, results in p k = 16.8 × 10 −11 exp(−234 K/T ) cm 3 s −1 for pure para-hydrogen and o k = 9.4 × 10 −11 exp(−101 K/T ) cm 3 s −1 for pure orthohydrogen.

Reaction of NH+, NH2+, and NH3+ ions with H2 at low temperatures

“…In recent experiments with our apparatus (Zymak et al 2013;Plašil et al 2012;Roučka et al 2018) and in other 22-pole ion trap experiments (Hauser et al 2015;Endres et al 2017) it has been confirmed that the collisional temperature (here denoted simply T ) is slightly higher than the temperature of the copper box surrounding the ion trap (nominal ion trap temperature, T 22PT ). At the present experimental conditions, we can safely assume that the collisional temperature in the interaction of ions with H 2 does not exceed the ion trap temperature by more than 10 K. For simplicity of presentation, we define the collisional temperature as T = T 22PT + 5 K with an uncertainty of ±5 K.…”

Reaction of N+ Ion with H2, HD, and D2 at Low Temperatures: Experimental Study of the Pathway to Deuterated Nitrogen-containing Molecules in the Interstellar Medium

“…For a particular experimental arrangement (construction of the ion trap), RF amplitude, and He pressure, the kinetic temperature of trapped ions can be obtained by measuring the Doppler broadening of absorption lines of trapped ions (Glosik et al 2006;Jusko et al 2014). Several recent experiments with linear 22-pole RF ion traps (Zymak et al 2013;Endres et al 2017;Roucka et al 2018) confirmed that the collisional temperature (T) can be slightly higher than T 22PT . On the basis of these studies, we can safely assume that under the present experimental conditions, the collisional temperature in the interaction of N + ions with HD and D 2 does not exceed T 22PT by more than 10 K. For the presentation of our data, we define the collisional temperature as T = T 22PT + 5 K with an uncertainty of ±5 K. In the context of the interaction of N + ions with HD and D 2 , we will simply use the term temperature interchangeably with collisional temperature.…”

Isotope Exchange Reaction of OH− Anion with HD at Temperatures from 15 K up to 300 K: Ion Trap Study

“…Some of these reactions were studied in our laboratory at temperatures below 300 K using a temperature-variable radio-frequency ion trap. Recently we studied the isotope exchange reactions OH − + D 2 and OD − + H 2 (Mulin et al 2015;Roučka et al 2018). Note that reaction (1) is the reverse of reaction (3).…”