Interaction of O− and H2 at low temperatures

Abstract

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.

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

“…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.…”

“…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.…”

Negative Ions in Space

“…The issue of achieving low collision energies is not as difficult for electron processes, in which the thermal velocities of neutral molecules are not an issue because the mass of the electron is so much lower and collision energies are very close to the energy of the electron. One experimental solution to these issues is to use a cryogenically cooled electrostatic ion trap; this technique was developed by Gerlich et al − Flow-tube methods in which the carrier gas undergoes expansion can also be used to achieve low temperatures . Recent advances in cooling atoms and molecules in magnetic and electric field traps are particularly interesting from the point of view of studying low-temperature processes relevant to cold astrophysical environments, but the trapping fields make it difficult to include charged particles in these experiments.…”

Complex formation and internal proton-transfer of hydroxyl-hydrogen anion complexes at low temperature

“…Several ion trap experiments have been carried out to study the cold chemistry of anions with neutrals at low temperatures down to about 10 K [16,21,42]. Recently chemical reactions and also inelastic collisions of the hydroxyl negative ion at temperatures below 20 K have been performed [33,43].…”