22-pole trap

Gerlich, D. (1995) Ion-neutral Collisions in a 22-pole Trap at Very-low Energies. Phys. Scripta T59 256-263. 

A state of the art trapping machine, the Atomic Beam 22-Pole Trap (AB-22PT) is shown schematically in Fig. 3.15. This instrument has been... 

Fig. 3.15. Schematic diagram of the Atomic Beam 22-Pole Trap Apparatus (AB-22PT). This instrument has been developed for exposing cold trapped ions to an effusive beam of H atoms. The velocity distribution of the hydrogen beam depends on the temperature of the accommodator and the transmission features of the two hexapole magnets. A short description of this setup has been given recently.A detailed documentation of this sophisticated instrument is in preparation. ...

Fig. 3.16. Temperature dependence of the ternary rate coefficients for the reaction He+ + 2He HeJ + He. The filled circles are data obtained with a 22-pole trap, the open squares have been measured using a selected ion drift tube. The fit fcs = 1.4 x 10 i(300 K/T)° cm /s is used as a thermometer . Note, however, that more precise experiments are needed in order to separate the influence of ion temperature, density of the neutrals and the temperature dependence of fea.

Important contributions towards a detailed state specific understanding of H-D exchange reactions in collisions of with H or H2 in all possible deuterated variants have been made in the last years in several laboratories. The activities, which all use low temperature 22-pole traps in combination with the method of laser induced reactions, have been summarized in Ref. 3. The feasibility of analyzing cold H3 via laser excitation, followed by proton transfer to Ar, has been first demonstrated in a compact trapping machine which has been mainly developed as an ion source. Meanwhile high power CW diode lasers are applied to excite ions and isotopic variants in specific states via overtone transitions. Also the first spectra with a free electron laser have been reported. ... 

Schlemmer S, Kuhn T, Lescop E, Gerhch D. (1999) Laser excited Nj in a 22-pole trap, experimental studies of rotational relaxation processes. Int. J. Mass Spectrom. Ion Proc. 185 589-602. 

The first 22-pole trap based apparatus has been described in detail elsewhere. Most of the early applications concentrated on the study of low temperature ion-molecule reactions (see Chapter 3). Of course in all these applications it is mandatory to have control over, or to get information on, the actual temperature of the stored species. Especially flexible are methods based on laser induced processes as discussed above. Selected laser induced reaction (LIR) schemes which can been performed with trapping machines have been summarized recently by Schlemmer et al. The sensitive method provides spectral information and rate coefficients for several competing... 

Some remarks concerning the reaction of N+( Pj) with H2 have been made in Chapter 3, more details can be found in Ref. 53 and references therein. Using reaction rate coefficients from phase space theory in which it has been assumed that translation, rotation and fine structure energy are equivalent, the competition between reactions 6.5 and 6.6 has been modeled. A few examples are plotted in Fig. 4 of Ref. 53. For the unknown relaxation rate coefficients k Pj Pj-i) = 10 "cm /s has been assumed with n = 9, 10 or 11. None of the calculated curves could reproduce the data measured in a 22-pole trap. 

Fig. 6.13. Test measurement for preparing N( Po)+ground state ions via inelastic collisions (fine structure relaxation) or chemical quenching at 15 K in a 22-pole trap. N+( Pi) ions which have been produced by electron bombardment with the high temperature population of the three fine structure states ( Pq Pi P2 = 1 3 5) are stored in normal hydrogen at a number density of 3 X 10 cm. The mono-exponential decay over 4 orders of magnitude indicates that the reaction rate coefficient for forming NH+ is independent on the finestructure state. For more details see text, Chapter 3 and Ref. 53.

A very successful installation of a temperature variable 22-pole trap has been made in Lausanne for the investigation of biologically related... 

Fig. 6.18. Rotational profile for the A IIg-X IIu transition of HCeH+ measured in the Basel 22-pole trap spectrometer. The comparison with the simulated spectrum shows that a rotational temperature of 30 K has been obtained. For the simulation a line width of 0.3 cm was used.

High-order linear traps, such as a 22-pole trap, have a relatively flat radial effective potential over most of the trap volume, which minimizes the contribution of the micro-motion to ion trajectories. In contrast, ions in a quadrupole exhibit wiggling motion almost everywhere along radial ion trajectories, as illustrated in Fig. 4. While this motion makes little difference for trapping ions, it turns out to be crucial for cryogenic cooling, as discussed below. 

An inverted version of the messenger tagging technique for detecting ion absorption uses the fact that electronic and/or vibrational excitation of ions hinders formation of weakly-bound clusters. This effect, explored years ago in relation to laser isotope separation [82], has recently been demonstrated for spectroscopy of N2" ions, cooled to 10.6 K in a 22-pole trap by collisions with He and termed laser-induced inhibition of cluster growth (LIICG) [83]. An electronic spectrum is generated by monitoring the reduction of the steady-state concentration of ion-He complexes as a function of the excitation laser wavenumber. 

Using this procedure. Red wine et al. obtained an upper limit for the temperature of 10-16 K for their 22-pole ion trap, consistent with what we measured in our 22-pole trap [46] as well as in a newly constructed cold octupole trap. In contrast, the 3-D quadrupole ion trap employed by Choi et al. attained temperatures of 45-54 K for protonated tyrosine [138], which is likely to reflect RF heating of the ions. 

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