Determining the energy distribution of electrons produced in associative detachment: The electron spectrometer with multipole trap

Rednyk

Kovalenko

et al. 2018

A&A

Self Cite

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.

Section: Methodsmentioning

confidence: 99%

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

Rednyk

Kovalenko

et al. 2018

A&A

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“…62,63 OH À or OD À ions are produced in the electron impact storage ion source using a mixture of N 2 O and H 2 or D 2 . 27,28 The desired ions are then selected by a quadrupole mass filter and guided into the trap, where they are stored. A He-D 2 or a He-H 2 gas mixture is introduced directly into the trap volume.…”

Section: Methodsmentioning

confidence: 99%

“…We recently studied H/D isotope effects in the reactions H À (D À ) + H and O À + H 2 (D 2 ) using the AB-22-pole ion trap apparatus 10,27,28 and we measured the temperature dependencies of their reaction rate coefficients for temperatures from 11 K up to 300 K. In the present study we investigate the H/D exchange process at a low temperature in a more complex collision system, OH À + H 2 and its isotopic variants, where isotopic exchange occurs via the H 3 O À complex and requires several chemical rearrangement steps. As such, this system is different from H/D exchange in many cation-molecule reactions.…”

Section: Introductionmentioning

confidence: 99%

H/D exchange in reactions of OH⁻ with D₂ and of OD⁻ with H₂ at low temperatures

Mulin

Phys. Chem. Chem. Phys.

Jusko

et al. 2015

Using a cryogenic linear 22-pole rf ion trap, rate coefficients for H/D exchange reactions of OH(-) with D2 (1) and OD(-) with H2 (2) have been measured at temperatures between 11 K and 300 K with normal hydrogen. Below 60 K, we obtained k1 = 5.5 × 10(-10) cm(3) s(-1) for the exoergic . Upon increasing the temperature above 60 K, the data decrease with a power law, k1(T) ∼T(-2.7), reaching ≈1 × 10(-10) cm(3) s(-1) at 200 K. This observation is tentatively explained with a decrease of the lifetime of the intermediate complex as well as with the assumption that scrambling of the three hydrogen atoms is restricted by the topology of the potential energy surface. The rate coefficient for the endoergic increases with temperature from 12 K up to 300 K, following the Arrhenius equation, k2 = 7.5 × 10(-11) exp(-92 K/T) cm(3) s(-1) over two orders of magnitude. The fitted activation energy, EA-Exp = 7.9 meV, is in perfect accordance with the endothermicity of 24.0 meV, if one accounts for the thermal population of the rotational states of both reactants. The low mean activation energy in comparison with the enthalpy change in the reaction is mainly due to the rotational energy of 14.7 meV contributed by ortho-H2 (J = 1). Nonetheless, one should not ignore the reactivity of pure para-H2 because, according to our model, it already reaches 43% of that of ortho-H2 at 100 K.

“…Stepan.Roucka@mff.cuni.cz energies down to 0.02 eV was carried out using a temperature variable flow/drift tube. 12 Furthermore, the kinetic energy distribution of the electrons produced in associative detachment has been studied by Mauer and Schulz, 13 Esaulov et al, 14 and Jusko et al 11 Using crossed beams, energy partitioning in the O − + D 2 → OD − + D reaction has been reported recently by Lee and Farrar. 15 The results of all these studies indicate high internal excitation of the produced H 2 O neutrals and slow electrons.…”

Section: Introductionmentioning

confidence: 98%

“…Other studies include the work of Claydon et al 9 and the detailed potential energy surface calculations of Werner et al 4 Experimental studies of the rate coefficients of reactions (1) and (2) and their temperature dependencies have been carried out before at room temperature and above using drift tubes, flowing afterglow, tandem mass spectrometry, and an octopole ion trap instrument. 10,11 A study at mean collision a) Author to whom correspondence should be addressed. Electronic mail:…”

Section: Introductionmentioning

confidence: 99%

Interaction of O− and H2 at low temperatures

Jusko

The Journal of Chemical Physics

Mulin

et al. 2015

Self Cite

Reactive collisions between O(-) and H2 have been studied experimentally at temperatures ranging from 10 K to 300 K using a cryogenic radiofrequency 22-pole ion trap. The rate coefficients for associative detachment, leading to H2O + e(-), increase with decreasing temperature and reach a flat maximum of 1.8 × 10(-9) cm(3) s(-1) at temperatures between 20 K and 80 K. There, the overall reaction probability is in good agreement with a capture model indicating efficient non-adiabatic couplings between the entrance potential energy surfaces. Classical trajectory calculations on newly calculated potential energy surfaces as well as the topology of the conical intersection seam leading to the neutral surface corroborate this. The formation of OH(-) + H via hydrogen transfer, although occurring with a probability of a few percent only (about 5 × 10(-11) cm(3) s(-1) at temperatures 10-300 K), indicates that there are reaction paths, where electron detachment is avoided.