Ion kinetics

Magnetic sector instruments typically operate with ion sources held at a potential of between 6 and 10 kV. This results in ions with keV translational kinetic energies. The ion kinetic energy can be written as zt V = Ifur and thus the ion velocity is given by the relationship... 

A) MASS-ANALYSED ION KINETIC ENERGY SPECTROMETRY (MIKES)... 

Accelerating voltage (high voltage) scan. An alternative method of producing a momentum (mass) spectrum in magnetic-deflection instruments. This scan can also be used, in conjunction with a fixed radial electrical field, to produce an ion kinetic energy spectrum. 

Ion kinetic energy spectrum. A spectrum obtained when a beam of ions is separated according to the translational energy-to-charge ratios of the ionic species contained within it. A radial electric field achieves separation of the various ionic species in this way. 

IKES. ion kinetic energy spectroscopy IRMS. isotope ratio mass spectrometry ISDMS. isotope dilution mass spectrometry ITMS. ion trap mass spectrometry LA. laser ablation... 

MIKES. mass-analyzed ion kinetic energy spectroscopy... 

The components A., B, P, Q,. .. may be atoms, molecules, or ions. Kinetic rates are sensitive to a host of factors that must be specified or inferred, such as temperature, pressure, and presence of inert solvent or active catalyst. Most often, a kinetic change is written so that there is an initial excess of reactants which decrease over time. 

The structure of the radical cation [CaHsN] (102) has been established by mass-analyzed ion kinetic energy spectrometry (MIKE) (780MS518). From structure (103), structures (104) and (105) are formed (Scheme 4). 

The high sensitivity and selectivity of the EPR response enables diamagnetic systems to be doped with very low concentrations of paramagnetic ions, the fate of which can be followed during the progress of a reaction. The criteria [347] for the use of such tracer ions are that they should give a distinct EPR spectrum, occupy a single coordination site and have the same valency as, and a similar diffusion coefficient to, the host matrix ion. Kinetic data are usually obtained by comparison with standard materials. 

After identifying the reactant ion, reaction cross-sections were measured as a function of average reactant ion kinetic energy. Q experimental is measured for given values of (eEl) 1/2 in the spectrometer, and experimental values of k... 

Intramolecular Isotope Effects. The data in Figure 2 clearly illustrate the failure of the experimental results in following the predicted velocity dependence of the Langevin cross-section. The remark has been frequently made that in the reactions of complex ions with molecules, hydrocarbon systems etc., experimental cross-sections correlate better with an E l than E 112 dependence on reactant ion kinetic energy (14, 24). This energy dependence of reaction presents a fundamental problem with respect to the nature of the ion-molecule interaction potential. So far no theory has been proposed which quantitatively predicts the E l dependence, and under these circumstances interpreting the experiment in these terms is questionable. 

Intramolecular isotope effect studies on the systems HD+ + He, HD+ + Ne, Ar+ + HD, and Kr + + HD (12) suggest that the E l dependence of reaction cross-section at higher reactant ion kinetic energy may be fortuitous. In these experiments the velocity dependence of the ratio of XH f /XD + cross-sections was determined. The experimental results are presented in summary in Figures 5 and 6. The G-S model makes no predictions concerning these competitive processes. The masses of the respective ions and reduced masses of the respective complex reacting systems are identical for both H and D product ions. Consequently, the intramolecular isotope effect study illuminates those... 

Figure 11. Ratio of experimental values of formation cross-section of CH0 + to calculated Langevin cross-section for collision of CH + with CH as a function of average ion kinetic energy...

With these ends in view, one of the principal objectives of research in ion-molecule reactions is to determine the dependence on ion kinetic energy of ion-molecule reaction rates. In the classical measurements of... 

Figure 10. Isotope effects in hydron transfer from CH2D2+ as a function of ion kinetic energy...

Mass-analysed ion kinetic energy spectrometry (MIKES) A form of MS-MS product-ion scan that may be carried out on a reversed-geometry double-focusing mass spectrometer. 

A complete model for the description of plasma deposition of a-Si H should include the kinetic properties of ion, electron, and neutral fluxes towards the substrate and walls. The particle-in-cell/Monte Carlo (PIC/MC) model is known to provide a suitable way to study the electron and ion kinetics. Essentially, the method consists in the simulation of a (limited) number of computer particles, each of which represents a large number of physical particles (ions and electrons). The movement of the particles is simply calculated from Newton s laws of motion. Within the PIC method the movement of the particles and the evolution of the electric field are followed in finite time steps. In each calculation cycle, first the forces on each particle due to the electric field are determined. Then the... 

From a comparison between the behavior of the microstructure parameter R (Fig. 44e) and the ion kinetic energy per deposited atom, max (Fig- 45b), it can be concluded that a one-to-one relation appears to exist between the relative strength of the ion bombardment, expressed in terms of max, and the microstructure parameter. This has also been suggested by others [246,422]. 

MIKES Mass-analysed ion kinetic energy spectrometry... 

Figure 11. Average ion kinetic energies as a function of cluster size for ammonia clusters and deuterated ammonia clusters resulting from Coulomb explosion of clusters. The average kinetic energies are obtained from the splittings in the cluster ion time-of-flight peaks see Figure 10. Taken with permission from ref. 90.

This system shows an induction period of about six hours before constant activity is attained during which the Ru3(C0)12 undergoes complete conversion to another ruthenium carbonyl complex. In situ nmr studies suggest this species to be the HRu2(C0)e ion. Kinetic studies show complex rate profiles however, a key observation is that the catalysis rate is first order in Pco at low pressures (Pcohigher pressures. A catalysis scheme consistent with these observations is proposed. 

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