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Studies of proton and deuteron transfer from methanium ions to various substrates and collision‐induced dissociation of isotopically substituted methanium ions suggest that under the low‐energy conditions of the ICR experiment, the addition of a hydrogen ion to methane produces a methanium ion whose hydrogens are structurally and chemically distinguishable. The reactions of methanium ions formed in the low energy electron impact ionization of CH4–CD4 mixtures are compatible with a methanium ion of Cs symmetry in which intramolecular rearrangement does not occur. Reaction studies on the methanium ions formed by the exoergic proton transfer from D3+ to methane indicate that rapid intramolecular rearrangements occur in these ions.

Four metastable ions from C2F6 and six metastable ions from C3F8 have been observed in a double focusing mass spectrometer. The metastable transitions are all endothermic and their occurrence is indicative of high internal excitation in the various fragment ions produced by electron impact ionization. The observed metastable transitions largely confirm those expected from studies of collision induced dissociation reactions in these same molecules by tandem mass spectrometry.

Spurious fragment peaks that simulate fragment‐ion dissociation products formed in the drift‐tube reaction region have been observed in a time‐of‐flight mass spectrometer adapted for kinetic studies of ion dissociation processes. These peaks arise from processes occurring after the reactant ion has passed through the reaction region and entered the potential barrier that is normally used to separate reactants and products by selectively shifting their flight times. The flight‐time shifts characteristic of such spurious peaks depend on the distance from the ion source to the potential barrier, whereas the shifts characteristic of normal fragment peaks are independent of this distance. Comparisons of experimentally measured flight‐time shifts with analytically calculated values identify a fragment peak observed in association with the N2+ mass‐28 peak in N2O as a spurious fragment peak, which represents not dissociation products of N2+ formed in the reaction zone, but neutrals formed inside the potential ba...

A mass spectrometer with a collision‐free modulated molecular beam sampling system was used to obtain the mass spectrum of N2F4 and to study ionization and dissociation processes in NF2 and N2F4. The mass spectrum of N2F4 differs significantly from previous studies, particularly in regard to the N2F4+/NF2+ ion intensity ratio, indicating that considerable decomposition had occurred in earlier work. Surprisingly, dissociation of N2F4 into NF2 radicals at 300°K at very low pressures, for which the degree of dissociation should be almost 100% at equilibrium, was found to be a slow process, an N2F4 molecule readily surviving the order of 105 wall collisions without decomposing. To obtain substantial conversion of N2F4 into NF2, it was necessary to send the sample through a heated line. Appearance potentials were determined for selected ions from N2F4 and NF2 and the relevant processes identified. The bond dissociation energy D(F2N–NF2)= 0.94± 0.1 eV= 21.6± 3.2 kcal/mole was directly obtained from the appearan...

The rate constants for the production of the secondary ions CO2H+, COH+, and N2H+ in gaseous mixtures of hydrogen with carbon dioxide, carbon monoxide and nitrogen have been measured by ion cyclotron resonance mass spectrometry. The results are similar to those of other techniques.

A time‐of‐flight mass spectrometer has been modified so that (1) the drift tube can be used as a reaction/collision chamber for kinetic studies of charge transfer, ion dissociation, and similar processes; and (2) ions can be produced in the source by either pulsed or continuous electron or photon beams. Variable potential barriers, produced in the drift tube by means of movable screened retarder grid assemblies, permit parent ions and fragment ions to be separated, identified, and measured after reaction times that are selectively variable within the range 7.197×10−3(m/q)12≤tr≤7.053(m/q)12 μsec, where m/q is the mass‐to‐charge ratio of the parent ions in amu per electron charge. The kinetic energy range is from 100 to 10 000 eV for positive ions and 3000 eV for negative ions. The residence time of ions within the ionizing region can be varied continuously from 0 to 100 μsec.

Ion cyclotron resonance spectroscopy has met with such wide acceptance that research groups utilizing this relatively new experimental technique now likely outnumber research groups which have used more traditional techniques, such as high pressure mass spectrometry, for the study of ion-molecule reactions. Since the previous review of ion-molecule reactions in Volume 1 9 o f the Annual Review of Physical Chemistry (1) there has been considerable development in the field. This development has been distributed among studies conducted with ion cyclotron resonance spectroscopy, drift tubes, high pressure mass spectrometry, flowing afterglows, tandem mass spectrometry, and beam experiments. Chemical applications of these techniques have been the subject of numerous recent reviews and monographs authored by principals in these investigations. In the present review an attempt will be made to chron­ icle the development of ion cyclotron resonance spectroscopy. Since this is the first review of the subject to appear in these volumes, the present article purports to be not only a review but an introduction as well. Sufficient back­ ground is developed to allow for a critical review of current experimentation in this field of endeavor. Ion cyclotron resonance spectroscopy is finding applications to the study of an increasing number of problems of general chemical interest. Recent developments promise an even wider range of applications. The technique is well suited for the routine study of ion-molecule reactions, which are readily identified using double resonance experiments (2). The identification of an ion-molecule reaction in a double resonance experiment provides useful information relating to the thermochemical properties of both ions and neu­ trals [including acidities (3-8) and basicities (9, 10) determined in the absence of complicating solvation phenomena], the identification of isomeric ion structures (1 1-16), and information concerning reaction mechanisms (17-23). Ion ejection techniques (11, 24) allow for the determination of product ion distributions in ion-molecule reactions even when other processes, such as

The positive and negative ions, formed by electron impact in perfluoromethyl cyclohexane, have been studied in a mass spectrometer. The observation of the most abundant positive ion CF3+ is in agreement with other studios, as is the appearance potential of this ion. Seven negative ions, the most abundant of which is the parent ion C7F14–, have been observed and possible mechanisms for their formation are discussed.

Kinetic energy spectra of H + ions produced by photodissociation of fast H + 2 ions by a ruby laser beam polarized either parallel of perpendicular to the ion beam are obtained. For the former polarization direction the spectrum shows a structure which reflects the vibrational levels of the primary ions which undergo dissociation.

The dissociation energy of F2 has been determined mass spectrometrically. The heat of formation of fluorine, ΔHf°(F), was determined from measurements of both the appearance potentials and translational energies of the products resulting from electron impact, including both positive and negative ions. One can derive values for the dissociation energy from each of the possible processes, namely: (1) dissociative electron attachment, (2) ion‐pair formation, and (3) dissociative ionization. The values are in excellent agreement and establish D°(F2)=37.5 ± 2.3 kcal/mol.

Mass spectrometric determination of vapor phase dissociation energies of scandium dicarbide and scandium tetracarbide

A reduction in the B–F bond dissociation energy is observed upon complexation of BF3 with ethyl ether.

One of the fundamental limitations in mass spectrometry arises in attempts to differentiate betwoeen atomic and nuclear ions having the same charge to mass ratio. Partial dissociation of complex ions in a mass spectrometer has been observed. By using a three-stage mass spectrometer, complete dissoclation of molecular ions has been achieved. The film acts as a strong force field at a discrete point in the beam trajectory causing uncorrelated forces to act on the constituent atoms of the molecules. Further experiments are in progress utilizing these films as well as thin nickel films. (A.C.)

Attention is drawn to a doubly-charged molecular ion of higher abundance than that of the singly-charged ion.