Dmytro Mulin

Stabilization of H+–H2 collision complexes between 11 and 28K

Formation of via association of H+ with H2 has been studied at low temperatures using a 22-pole radiofrequency trap. Operating at hydrogen number densities from 1011 to 1014 cm−3, the contributions of radiative, kr, and ternary, k3, association have been extracted from the measured apparent binary rate coefficients, k*=kr+k3[H2]. Surprisingly, k3 is constant between 11 and 22 K, (2.6±0.8)×10−29 cm6 s−1, while radiative association decreases from kr(11 K)=(1.6±0.3)×10−16 cm3 s−1 to kr(28 K)=(5±2)×10−17 cm3 s−1. These results are in conflict with simple association models in which formation and stabilization of the complex are treated separately. Tentative explanations are based on the fact that, at low temperatures, only few partial waves contribute to the formation of the collision complex and that ternary association with H2 may be quite inefficient because of the ‘shared proton’ structure of .

Interaction of O− and H2 at low temperatures

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.

Electron Transfer and Associative Detachment in Low-Temperature Collisions of D– with H

The interaction of D(-) with H was studied experimentally and theoretically at low temperatures. The rate coefficients of associative detachment and electron transfer reactions were measured in the temperature range 10-160 K using a combination of a cryogenic 22-pole trap with a cold effusive beam of atomic hydrogen. Results from quantum-mechanical calculations are in good agreement with the experimental data. The rate coefficient obtained for electron transfer is increasing monotonically with temperature from 1 × 10(-9) cm(3) s(-1) at 10 K to 5 × 10(-9) cm(3) s(-1) at 160 K. The rate coefficient for associative detachment has a flat maximum of 3 × 10(-9) cm(3) s(-1) between 30 and 100 K.

Reactions of O− with D2 at temperatures below 300 K

The reaction of O− anions with molecular deuterium D2 has been studied experimentally using a cryogenic 22-pole radiofrequency ion trap. Two reaction channels were observed. In the associative detachment D2O and an electron are formed and for atom transfer formation OD− + D was observed. The rate coefficients of the reactions have been determined at temperatures below 300 K. The reaction rate coefficient k 1 of the associative detachment increases with decreasing temperature from k 1(300 K) = 0.5 × 10−9 cm3 s−1 at 300 K up to k 1(70 K) = 1.2 × 10−9 cm3 s−1 at 70 K both with 30 % overall uncertainty.

Reactions of O− with D2 at low temperatures 10 − 300 K

Energetically possible are also reactions leading to the formation of metastable D2O anion in three body or radiative association. However these processes have not been detected experimentally. Studies of gas-phase processes involving water and especially those leading to isotopic fractionation [1] is essential for understanding of the water formation in the Universe. The reactions were studied using a 22-pole radiofrequency ion trap. It was mounted on a cryo-cooler in an ultra-high vacuum system. The measuring procedure was based on iterative filling of the trap with a well-defined number of primary ions O where they react with molecular deuterium. The content of the trap were analyzed after chosen times using a quadrupole mass spectrometer and a micro-channel plate detector. Further detail may be found in [2] and references therein. We studied previously analogous reactions involving O and H2. At first we measured electron energy spectrum originating from associative detachment [3] at 300 K. Later on we studied both reactions using the 22-pole ion trap [4]. Very interesting dependence on temperature is shown on Figure 1. Up to now the associative detachment has been measured mostly at temperatures higher than 300 K and the observed reaction rate coefficient was about 1⁄3 of the Langevin rate. It is explained by the fact that trajectories on only one of three electronic surfaces of the collision system can lead directly to autodetachment. At lower temperatures we observed unexpectedly high value of the associative detachment rate coefficient. Theoretical model in our paper [4] for the reaction O + H2 explained this behavior by rearrangement of the collisional system in a shallow local minimum. The increase of the reaction rate coefficient at low temperatures is in qualitative agreement with the theoretical predictions. The presented data will be compared with classical trajectory simulation model. An isotopic effect will be evaluated.

Ion trap study of the charge transfer and associative detachment reactions of D− + H

The thermal rate coefficients of the associative detachment and charge transfer reactions of D− + H have been measured at temperatures below 160 K. The measurements have been carried out using a cryogenic 22-pole ion trap, combined with a beam of atomic hydrogen - the AB-22PT instrument.

Reaction of NH+with atomic hydrogen at low temperatures - an experimental study

The reaction of NH+ with H was studied at temperatures below 200 K. Using an rf-trapping technique, NH+ ions were confined, cooled and exposed to a beam of thermalized atomic hydrogen.

Formation of NH+ in collisions of N+ with para- or ortho-H2 at low temperatures – an experimental study

Using a radiofrequency ion trap at low temperatures, an experimental study of collisions of N+ with or-tho/para-H2 is reported.

Interactions of H? Anions with Atomic Hydrogen?Ion Trap study at 10?100 K

Results of an experimental study of the associative detachment reaction H + H− → H2 + e− and a description of the ion trap apparatus combined with a variable temperature beam of atomic hydrogen are presented.