Ion-trap experiment

The reactions of the gold anion Au- and of the di- and triatomic gold cluster monoanions Au2- and Au3- with CO were studied in a radio-frequency octopole ion trap experiment at cryogenic temperatures. Au- shows no affinity for CO, but the two cluster anions absorb up to two CO molecules. Particular stability has been ascribed to [Au3(CO)2]-, for which the binding energy has been estimated from thermolysis rate coefficients.292... 

Fig. 17.9 Sketch of a typical setup for ion trap experiments on lasing microdroplets. The oscillating field between the inner and outer ring electrodes forms the trapping potential, and gravitational forces can he opposed by static electrical fields to move the droplet to the trap center with no micromotion...

For are (NO+), however, the situation is not so clear. The 300 K value is well established (are (NO+) = 4.3 x 10-7 cm3 s-1)192, 201 but serious disagreement exists between the Te dependence of are (NO+) obtained from the SA experiment of Huang et al.1951 and the ion trap experiment of Walls and Dunn1991 which give Ore (N0+) T 0,37 and T 0-83 respectively. The recently reported Te dependence by Torr et al.2021 deduced from the night-time AE satellite observations strongly favours that obtained using the ion trap experiment. In a very recent review paper,... 

As the experiment is operating in the kinetic low-pressure regime, the decomposition rate constant can consequently be considered to be much larger than the stabilization rate constant term k fcs[He]. This leads to a simplified expression for the termolecular rate constant, which can be applied to the experimental conditions present in the ion trap experiment... 

Coadsorption phenomena in heterogeneous catalysis and surface chemistry quite commonly consider competitive effects between two reactants on a metal surface [240,344]. Also cooperative mutual interaction in the adsorption behavior of two molecules has been reported [240]. Recently, this latter phenomenon was found to be very pronounced on small gas-phase metal cluster ions too [351-354]. This is mainly due to the fact that the metal cluster reactivity is often strongly charge state dependent and that an adsorbed molecule can effectively influence the metal cluster electronic structure by, e.g., charge transfer effects. This changed electronic complex structure in turn might foster (or also inhibit) adsorption and reaction of further reactant molecules that would otherwise not be possible. An example of cooperative adsorption effects on small free silver cluster ions identified in an ion trap experiment will be presented in the following. 

Cooperative Coadsorption Effects on Small Gold Clusters. Two examples of cooperative adsorption effects on small gold cluster anions identified in temperature dependent rf-ion trap experiments (see Chemical and Catal3dic Properties of Gas-Phase Clusters for experimental details) will be presented in the following. Au3 does not react with O2 in the ion trap experiment at any reaction temperature [34]. It, however, adsorbs a maximum of two CO molecules at reaction temperatures below 250 K [185]. If the gold trimer is exposed simultaneously to CO and O2 inside the octopole ion trap, still no reaction products are observed at reaction temperatures above 250 K as can be seen... 

The reactivity of the clusters can then be studied by various experimental techniques, including fast flow reactor kinetics in the postvaporization expansion region of a laser evaporation source [21, 22], ion flow tube reactor kinetics of ionic clusters [23, 24], ion cyclotron resonance [25, 26], guided-ion-beam [27], and ion-trap experiments [28-30]. Which of these techniques is applied depends on the charge state of reactants (neutral, cationic, anionic), on whether the clusters are size-selected before the reaction zone, on single or multiple collisions of the clusters with the reactants, on the pressure of a buffer gas if present, and on the temperature and collision energy of the reactant molecules. 

Many similar applications of quadrupole linear ion trap instruments have been reported [320-322,329,330], As discussed above, the Q-Trap is a triple quadrupole mass spectrometer capable of performing QMF type and 2D ion trapping experiments. This mass spectrometer can be operated exclusively in the QMF mode, as with a conventional QMF, or it can be operated exclusively in the ion trapping mode similar to a conventional 2D ion trap mass spectrometer. Advantages of using a Q-Trap mass spectrometer over a conventional QMF mass spectrometer come into play when one is attempting to perform both quantitative and qualitative metabolite detection/identification experiments from a single injection rather than separate... 

Guide, S. Rotter, D. Barton, P. Schmidt-Kaler, F. Blatt, R. Hogervorst, W. Simple and efficient photo-ionization loading of ions for precision ion-trapping experiments. Appl. Phys. B. 2001, 73, 861-863. 

In the internal ionization mode, ions are formed, stored, and excited resonantly to the point of ejection inside the ion trap in the presence of neutral sample molecules. Primary fragment ions confined in the ion trap experience the flow of neutral sample molecules through the ion trap for a period of time that varies from cfl 2 ms to ca 200 ms. The longer is this period of time, the greater is the probability of the occurrence of undesirable ion/molecnle reactions this process is known as self-chemical ionization, or self-Cl [20], Typically, self-CI will create [M -H H] + ions due to proton transfer. However, adduct ion peaks may be formed when an alkyl group is transferred. The self-CI process may affect library-search results of those compounds because the majority of mass spectra in mass-spectral libraries were acquired with quadru-pole mass filters or magnetic sector mass spectrometers wherein self-CI does not... 

A similar ion trap experiment was performed with Be ions. The ions were cooled via the 2s Si/2(M/ = -3/2, Mj = -1/2) - 2p /2( -3/2, -3/2) transition at A = 313 nm with a frequency doubled dye laser, and were additionally optically pumped in the ground state. Measurements of the axial (I z), magnetron (v ), and electric field shifted cyclotron (Vc)frequencies of the stored ions provide the free-space cyclotron... 

Figure 17. Configuration of a laser-microwave ion trap experiment after Refs. 94 and 98.

The CH3 + H2 data from two different experiments are enigmatic. The low pressure ion trap experiment of Barlow, Dunn, and Schauer (I984a,b) has been claimed by Bates (1986d) to have the ions at an effective temperature much h her than the 13 K of the ambient gas. He deduced a stabilization rate kj. of 3.5(4) s T This value of k- leads to a radiative association rate kj. of 3(-13) cm s at 80 K, the temperature in the mgh pressure trap experiment of Gerlich and Kaefer (1988). However, the value of delennined by Gerlich and Kaefer (1988), again a preliminary value, is less than 3(-15) cm s which is almost two orders of magnitude lower. 

Fig. 3.23. Temperature dependence of the rate coefficient for the reaction C2HJ+H2 —> C2H + H. As discussed by Gerlich, there is some disagreement between the free jet and the ion trap experiments. While, at low temperatures, the high pressure experiments seems to indicate an increasing rate coefficient, the 10 K ion trap results proof that the rate coefficient for the abstraction reaction is much smaller than 10 cm s . A possible explanation is the fast radiative association process (fcr(p-H2) = 5 X 10 cm s ), which has been observed in the ion trap experiment (open circle and triangle). The phase space calculations (solid line) have used adjusted parameters for getting the low temperature behavior.

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