The destruction of CH+ ions in collisions with H atoms has been studied in a temperature-variable 22 pole ion trap (22PT) combined with a cold effusive H-atom beam. The stored ions are relaxed to ...temperatures of T 22PT >= 12 K. The hydrogen atoms, produced in a radio frequency discharge, are slowed down to various temperatures of T ACC >= 7 K. They are formed into an effusive beam. The effective density of the hydrogen atoms in the trap as well as the H2 background are determined in situ using chemical probing with CO2 +. The experimental arrangement allows us not only to measure thermal rate coefficients (T 22PT = T ACC), but also to extract state-specific rate coefficients k(J,T t) at selected translational temperatures T t and for the CH+ rotational states J = 0, 1, and 2. The measured thermal rate coefficients have a maximum at 60 K, k = (1.2 ? 0.5)X10--9 cm3 s--1. Toward higher temperatures, they fall off in accordance with previous measurements and the trend predicted by phase space theory. Toward lower temperatures, the rate coefficients decrease significantly, especially if the rotation of the ions is cooled. At the coldest conditions achieved (beam: 7.3 K; trap: 12.2 K), a value as low as (5 ? 4) X 10--11 cm3 s--1 has been measured. This leads to the conclusion that non-rotating CH+ is protected against attacks of H atoms. This surprising result is not yet understood. It is most probably due to quantum-dynamical effects already occurring at large distances.
Synopsis The reaction of dication C++ with H2 was studied at temperature 20 K using a linear 22-pole radiofrequency ion trap. The overall reaction rate coefficient was measured as 1.4 ± 0.3 × 10−10 ...cm3 s−1. The upper limit for formation of CH+ in this reaction was evaluated as 4 × 10−12 cm3 s−1.
State Specific Stabilization of H+ + H2(j) Collision Complexes Gerlich, D; Plašil, R; Zymak, I ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
10/2013, Letnik:
117, Številka:
39
Journal Article
Recenzirano
Stabilization of H3 + collision complexes has been studied at nominal temperatures between 11 and 33 K using a 22-pole radio frequency (rf) ion trap. Apparent binary rate coefficients, k * = k r + k ...3H2, have been measured for para- and normal-hydrogen at number densities between some 1011 and 1014 cm–3. The state specific rate coefficients extracted for radiative stabilization, k r(T;j), are all below 2 × 10–16 cm3 s–1. There is a slight tendency to decrease with increasing temperature. In contrast to simple expectations, k r(11 K;j) is for j = 0 a factor of 2 smaller than for j = 1. The ternary rate coefficients for p-H2 show a rather steep T-dependence; however, they are increasing with temperature. The state specific ternary rate coefficients, k 3(T;j), measured for j = 0 and derived for j = 1 from measurements with n-H 2 , differ by an order of magnitude. Most of these surprising observations are in disagreement with predictions from standard association models, which are based on statistical assumptions and the separation of complex formation and competition between stabilization and decay. Most probably, the unexpected collision dynamics are due to the fact that, at the low translational energies of the present experiment, only a small number of partial waves participate. This should make exact quantum mechanical calculations of k r feasible. More complex is three-body stabilization, because it occurs on the H5 + potential energy surface.
We present results of plasma afterglow experiments on ternary electron-ion recombination rate coefficients of H3 + and D3 + ions at temperatures from 50 to 300 K and compare them to possible ...three-body reaction mechanisms. Resonant electron capture into H3* Rydberg states is likely to be the first step in the ternary recombination, rather than third-body-assisted capture. Subsequent interactions of the Rydberg molecules with ambient neutral and charged particles provide the rate-limiting step that completes the recombination. A semiquantitative model is proposed that reconciles several previously discrepant experimental observations. A rigorous treatment of the problem will require additional theoretical work and experimental investigations.
•Instrument for measuring the energy of electrons produced in ion trap.•Calibration with electrons from photodetachment.•Energy distribution of electrons from associative detachment.
Design of a ...novel instrument for the analysis of the kinetic energy of the detached electrons is presented. The electron spectrometer with multipole trap combines a radiofrequency ion trap with a magnetic adiabatic collimation filter and is capable of measuring the energy of electrons produced in the trap. The theory of operation and numerical simulations of the instrument are presented together with a proof of concept measurements using three different mechanisms of electron production – thermionic emission from a tungsten filament; laser photodetachment from O− anions; associative detachment of O− + H2, D2, and CO.
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