Ion Cyclotron Resonance Cell Research Articles

Mass and energy selective ion partitioning in a two-section Fourier-transform ion cyclotron resonance spectrometer cell

A method for ion isolation due to selective partitioning in a two-section Fourier transform ion cyclotron resonance cell is described. The limitation on ion cyclotron radius imposed by the conductance limit aperture is exploited to isolate ions. This method allows ions to be isolated according to: (i) mass, (ii) translational energy in the cyclotron orbit, and (iii) spatial location. The general utility of the technique for ion-molecule studies is discussed, and extension to analytical applications is straightforward.

Association reactions at low pressure. I. Collision-stabilized association below 1 micron

Rate coefficients for collision-stabilized association of a protonated ion AH + and its parent molecule A to form the proton bound dimer A 2H + were measured in an ion cyclotron resonance (ICR) cell at room temperature for the systems where A  dimethyl ether and acetonitrile. Third-order rate coefficients are reported for the dimethyl ether system with the third bodies (CH 3) 2O, Ar, N 2, Ne, He, and for the acetonitrile system with the third bodies CH 3CN, N 2, Ne, and He. A selected ion flow tube (SIFT) study on these same systems provides evidence that the rate coefficient, k f, for (A 2H +)* formation may be less than the collision rate, k c. The lifetimes of the collision complex (A 2H +)* are ≥ 0.5 × 10 −6 s. A consequence of k f < k c is that derivation of the average lifetime of (A 2H +)* with respect to unimolecular decomposition from the third-order rate coefficient may generally lead to values that are too small.

An ion cyclotron resonance spectrometer as a gas chromatographic detector. The effect of continuous trapping on performance

Use of an ion cyclotron resonance (ICR) mass spectrometer in the continuous trapping mode as a detector for a gas chromatograph (GC) is illustrated. The long residence time of the ions in the ion source makes ion/molecule reactions inherent to the technique. These reactions are useful in aiding in the identification of samples eluting from the GC. Furthermore, under the continuous trapping conditions, the spectra are pressure-independent. Factors governing the mass resolution of the ICR spectrometer and chromatographic resolution of the GC-ICR combination are evaluated. In so doing, a closed-form expression is derived for the residence time of an ion in a trapping ICR cell.

Negative ion forration by attachment of electrons to radicals studied by ion cyclotron resonance spectrometry

It is suggested that some negative ions are formed by attachment of secondary electrons to radicals resulted from positive ion-molecule reactions. The process has been studied using an ion cyclotron resonance cell equipped with venetian-blind type trapping electrodes. A trapping voltage modulation technique was developed to obtain the positive ion signal in the double resonance spectra of negative ion. Formation and solvation of OH − in water vapor have been studied.

Equilibrium and double resonance in the unquenched mode in trapped ion cyclotron resonance spectrometry

If a MeIver-type trapped ion cyclotron resonance (ICR) cell is used without a quenching pulse, a steady-state abundance of ions is achieved, based on a balance between production and coIlisional ion loss to the walls. The intensity of mass signals in this unquenched mode is shown to be related to the kinetic and equilibrium parameters involved, although not in a linear fashion. Double resonance signals have meaning in certain cases. All transient intermediates and many slowly formed products are observed when using this mode.

Electron photodetachment from HS−. The electron affinity of HS

The cross section for electron photodetachment from H${\mathrm{S}}^{\ensuremath{-}}$ has been measured using an ion cyclotron resonance (ICR) spectrometer with a tunable dye laser. A cubic spline routine is employed to remove random noise from the spectrum and allows the observation of rotational effects. The structure in the spectrum is explained in terms of a model which includes the interaction of the spin, orbital, and rotational angular momenta in HS. Comparison of the theoretically constructed photodetachment cross section predicted by this model with the experimental spectrum leads to an electron affinity for HS of 2.314\ifmmode\pm\else\textpm\fi{}0.003 eV and an estimate of the rotational temperature of the H${\mathrm{S}}^{\ensuremath{-}}$ ions in the ICR cell.

Electron impact studies: CXXXI—Ion cyclotron resonance studies of ambident nucleophiles. The reaction between the thioacetate anion and thioacetic anhydride. A further example of a negative ion McLafferty rearrangement

AbstractThe [MeCOS]− ion undergoes reaction with neutral thioacetic anhydride in an ion cyclotron resonance cell to yield an adduct [M+MeCOS]− which decomposes principally by loss of CH2CS, thus establishing the occurrence of nucleophilic attack through O at the carbonyl centre.

Signal modeling for ion cyclotron resonance

A new signal model, called the rotating electric monopole signal model, is developed for ion cyclotron resonance (ICR) experiments. Unlike prior signal models, the model is applicable to all forms of ICR spectroscopy which use radio-frequency detection methods. The signal model consists of a rotating electric monopole which is shown to be equivalent for signal generation purposes to a rotating electric dipole and for a macroscopic number of ions to a rotating electric polarization. The rotating polarization induces an alternating charge in the plates of the ICR cell and an alternating current between and an alternating voltage across the plates of the ICR cell. A noise analysis is performed, and if amplifier noise is neglected, the ICR sensitivity according to the model is found to be inversely proportional to the ion mass. This is the same sensitivity dependence as is found with conventional ICR power absorption experiments. The ICR voltage signal strength is inversely proportional to ion mass if the monitoring circuit is predominantly resistive and is independent of ion mass if the circuit is predominantly capacitive. The model clearly illustrates the parallelism between signal generation in ICR spectroscopy and signal generation in other coherent radiation spectroscopies such as NMR and microwave spectroscopy.

Characterization of intensity oscillations in trapped-ion cyclotron resonance spectra

Analyses of electrostatic fields and ion motion for a hybrid drift-trapping ion cyclotron resonance cell are presented. The frequency of motion in the ion trap is used to explain the oscillations in signal intensity as a function of ion-trapping time occasionally observed in this type of trapped-ion cyclotron resonance cell.

New design of an ion cyclotron resonance cell capable of temperature variation over the range 80⩽T⩽450 K

The design of an ICR cell capable of convenient operation over the temperature range 80< or =T< or =450 K is reported. Time-temperature plots indicate that the cell can undergo changes in temperatures of DeltaT=100 K in 30-45 min. Thermal gradients in the cell are small, less than +/-2 K. Factors that governed the design of the cell are discussed in detail, as are potential problem areas. The cell is tested by measuring two proton transfer equilibrium constants, one that shows a large temperature coefficient and the other a small temperature coefficient. In each case the results agree well with similar experimental data in the literature.

Luminescence in near-thermal charge exchange, I: He++N2

A pulsed Ion Cyclotron Resonance cell fitted with synchronous photon-counting equipment is used to study the emission produced by near-thermal (≲0.1

Quantum-theoretical treatment of motions of ions in ion cyclotron resonance cells

A quantum-mechanical treatment of the power absorption of ICR ions based on a minimized wavepacket-approach is presented. With the aid of minimum wavepackets constructed using the exact wavefunctions for the ion motions in a homogeneous magnetic field, the power absorption of the ions in cyclotron resonance has been treated within the framework of the linear response theory. The result agrees with that obtained according to the projection-operator formalism.

Measurement of the angular distribution and energy of ionic fragments from photodissociation of molecular ions

A theoretical analysis of the trapping efficiency of photofragment ions formed by polarized and unpolarized radiation is developed for the ion cyclotron resonance cell. The analysis outlines a prescription for estimating the kinetic energy and anisotropy of the angular distribution of fragment ions and is found to agree well with experiments performed on the H 2 + molecular ion. With a photodissociation wavelength of 5790 Å the cross section for formation of H + from H 2 + is found to be 6.8 × 10 −19 cm 2 and the average kinetic energy of the protons was estimated as 0.7 eV. In the light of these results use of the ICR technique for such measurements is evaluated.

Ion velocity distributions in an ICR spectrometer and their effect on measured rate constants

The translational velocity distributions of ions formed by electron impact in both square and flat ion cyclotron resonance (ICR) cells are theoretically determined. These velocity distributions result from acceleration of the ions in the trapping field of the spectrometer. ICR rate constants are computed from these distributions assuming the reaction cross section is proportional to v−n. The computations are compared to thermal values for a range of n and for a range of trapping voltages. In the most severe cases the ICR rate constants are predicted to deviate from thermal values by ∼20%. The analysis considers only reactions occurring immediately following ion formation in the electron beam. Collisions with unreactive species will, of course, rapidly transform the ICR distribution to the thermal distribution. The effect of ion mass on the velocity distribution functions and rate constants was explicitly studied. The effects on the velocity distributions may be appreciable in extreme cases but the effect on the predicted ICR rate constants is small.

Rate constant measurement for the reaction of D 3+ with H 2

The rate constant and the product distribution for the reaction of D 3 + with H 2 has been measured as a function of the D 3 + vibrational energy. In these experiments a mass analyzed beam of D 3 + ions is decelerated to less than 0.1 eV and is subsequently injected into an ion cyclotron resonance (ICR) cell where reaction with H 2 may occur. Ion detection is achieved using a conventional oscillator-detector. The number of D 3 +-D 2 coliisions was varied from 0 to 10 by changing the D 2 pressure in the source of the first stage of the instrument.

The interaction of ions with nonpolar neutrals: The collision broadening of ion cyclotron resonance lines of ions in hydrogen and methane

The motion of ions in an ion cyclotron resonance cell is considered, and measurements of ion cyclotron resonance linewidths are described. The connection between cyclotron resonance linewidths and kinetic parameters is developed. Mobilities and collision frequencies of CH5+, C2H5+, C3H7+, C4H9+, and Na+ in methane and H+, H3+, H30+, CH5+, C2H5+, C3H7+, and Na+ in hydrogen are determined from the linewidth measurements. Resulting mobilities of H+, H3+, and Na+ in H2 are found to agree well with drift tube measurements, in contrast to previous cyclotron resonance linewidth determinations. The mobilities are interpreted in terms of three model ion molecule interaction potentials. The mobilities are found to be in general consistent with both a three term 12–6–4 potential and an acentric potential but not with the simple polarization potential. Potential parameters consistent with binding energies from the literature and the present mobility measurements are reported for H3+–H2, CH5+–CH4, and C2H5+–CH4.

1353. Analysis of ion motion in ion cyclotron resonance cells: T F Knott and M Riggin, Can J Phys, 52 (5), 1974, 426–435

1353. Analysis of ion motion in ion cyclotron resonance cells: T F Knott and M Riggin, Can J Phys, 52 (5), 1974, 426–435

Theory of Ion Cyclotron Resonance

A theoretical analysis is given of the most commonly used type of ion cyclotron resonance (ICR) spectrometer, which has a cell of rectangular cross section. Though the equations of motion of the ions in this cell are extremely nonlinear, it has been possible to simplify the analysis by exploiting the facts that the longitudinal oscillations in the trapping potential are approximately decoupled from the cyclotron motion and that the cyclotron frequency [Formula: see text] the trapping oscillation frequency [Formula: see text] the spread of instantaneous cyclotron frequencies in the trap. A method is described for constructing an ensemble of ions appropriate to the mechanism of ion production and to the various drift and trapping voltages employed in the ICR cell. Line shapes are calculated in the collisionless regime. An ad hoc "average ion" model is presented, which simplifies the analysis of the spatial distribution of the ions through the dependence of the effective ICR frequency and line width on cell voltages and dimensions. Finally, an explicit distribution function is derived for the ion kinetic energy in the cell. The effect of a uniform RF electric field at resonance is shown to increase not only the average kinetic energy, but the spread of energies as well. A substantial spread of energies is also produced by the trapping oscillations. The breadth of the kinetic energy distribution complicates the interpretation of energy dependent processes using ICR under conditions normally used up to now. Some improved techniques for the study of energy dependent cross sections are proposed.

Analysis of Ion Motion in Ion Cyclotron Resonance Cells

The detailed discussion of ion motion in ion cyclotron resonance cells forms the basis of any interpretation of experimental results. We show that the resonance frequency of (quasi-) cyclotron motion is a function of the ion's position in the cell, and that its drift velocity exhibits a similar dependence. These features of the motion are due to the complicated multipole structure of the electric field. In spite of this, we find simple expressions for the ion coordinates as functions of time.

Dependence of ion cyclotron resonance on cell parameters

The ion cyclotron resonance (ICR) frequency and line width have been measured as a function of cell voltages and ionizing electron beam current. These measurements can be understood quantitatively in terms of a detailed model for the drift and oscillatory motion of the ions in the rather complicated electric field distribution of the ICR cell.