Cyclotron Resonance Techniques Research Articles

Selective optical valley pumping in silicon and germanium

The preferential population of conduction band valleys in Si and Ge was observed at T = 1.8° K with linearly polarized optical excitation of crystals via indirect and direct transitions. The concentration of the photoelectrons in valleys was measured by the cyclotron resonance technique.

Trapped ion cyclotron resonance studies of symmetric electron- and proton-transfer reactions

Trapped ion cyclotron resonance techniques have been used to study symmetric electron-transfer processes involving N 2, CO and CO 2 and symmetric proton-transfer processes involving H 2, CH 4 and NH 3. In most cases these reactions have been found to be fast and can be shown to be a very effective means of momentum transfer and energy relaxation. Comparisons of experimental and theoretical rate constants have been used to deduce models for electron- and proton-transfer reactions.

ChemInform Abstract: GAS PHASE ION CHEMISTRY OF 2‐FLUOROPROPANE BY ION CYCLOTRON RESONANCE SPECTROSCOPY

The gas phase ion chemistry of 2-fluoropropane is reported. The parent ion fragments to yield (CH/sub 3/)/sub 2/CF/sup +/, CH/sub 3/CHF/sup +/, and CH/sub 2/CHF/sup +/ as the abundant primary ions, all of which react with the parent neutral by F/sup -/ transfer to yield (CH/sub 3/)/sub 2/CH/sup +/ (CH/sub 3/)/sub 2/CH/sup +/ in turn reacts with the parent neutral by H/sup -/ transfer to regenerate (CH/sub 3/)/sub 2/CF/sup +/, thus completing a chain reaction which leads to the conversion of 2-fluoropropane to a mixture of propane and 2,2-difluoropropane via ionic intermediates. This chain reaction is terminated by a slow condensation reaction of C/sub 3/H/sub 7//sup +/ with 2-fluoropropane to yield C/sub 6/H/sub 13//sup +/. A variety of trapped ion cyclotron resonance techniques, including in particular cyclotron resonance ion ejection methods, permits all of the rate constants for this reasonably complex reaction scheme to be extracted. 21 references, 2 figures, 3 tables.

Slow metastable transitions in aromatic species

AbstractA tandem Dempster‐ion cyclotron resonance mass spectrometer was used to examine metastable transitions in benzene, toluene, anisole and anisole 1,3,5‐d3. The tandem‐ion cyclotron resonance technique examines all unimolecular reactions of the injected, mass‐selected ion, which occur between the injection time of several microseconds and the ion cyclotron resonance reaction section residence time of several milliseconds. The long sampling interval results in different relative intensities and considerably larger isotope effects than have been observed in previous studies.

Ion-molecule reactions in H 2/rare-gas systems by ion cyclotron resonance I. Reactions with He and Ne

Ion cyclotron resonance (ICR) techniques have been applied in a detailed study of ion-molecule reactions in hydrogen/rare-gas systems. Absolute rate constants are reported for both the total rate of reaction as well as for each of the possible reaction channels for reaction of H 2 + with X and X + with H 2, where X is either helium or neon. The average translational energy of the reactant ions is less than 0.1 eV, and thus these rate constants are indicative of reaction of ions whose translational energy may be considered as approximately thermal. The energy dependence of the total rate of reaction was measured using a new technique which is based on the ability to energize an ion in the source and observe ions of the same mass in the analyzer. Additionally, the rate constants for each reaction channel were measured using standard double-resonance methods. Isotope effects, as reflected in the product-ion ratio XH +/XD + of reaction products from the reaction of HD + with He and Ne, were also examined as a function of energy. The results are compared with theoretical predictions and with previous experimental studies.

Ion-molecule reactions in H 2/rare-gas systems by ion cyclotron resonance II. Reactions in systems of H 2 with Ar, Kr and Xe

Experimental ion cyclotron resonance techniques described in the companion paper have been used to measure rate constants for reaction of hydrogen ions (H 2 + or D 2 +) with argon, krypton and xenon as well as for reaction of Ar +, Kr + and Xe + with hydrogen or deuterium. For the conditions of lowest energy, the average translational energy is less than 0.1 eV; thus these rate constants are representative of reactions of ions whose translational energy is approximately thermal. The energy dependence of the total rate of reaction was measured using a new technique which is based on the ability to energize an ion in the source and observe ions of the same mass in the analyzer. Rate constants for each reaction channel were measured using standard double resonance methods. Isotope effects, as reflected in the ArH +/ArD + ratio are given as a function of ion energy. The results are compared with previous experimental and theoretical results.

Ion-molecule reactions of substituted cyclopropanes by ion cyclotron resonance spectroscopy

The gas phase ion chemistry of cyclopropane and a variety of its monosubstituted derivatives (c-C/sub 3/H/sub 5/X, with X = H, Cl, NH/sub 2/, CN, OH, and COCH/sub 3/) has been investigated utilizing ion cyclotron resonance techniques. Reactions of ions with cyclopropane involve most prominently formation of a reaction intermediate from which loss of ethylene and to a lesser extent loss of methyl or ethyl radical occurs. The ion chemistry of substituted cyclopropanes is dominated entirely by the substituent and is markedly different from cyclopropane. In addition to the increased prominence of the protonated parent ion and its corresponding association products, loss of neutrals HX (e.g., HCl) from reaction intermediates becomes significant. Ion-molecule reaction rate constants are extracted and compared for the important reaction pathways of each of the cyclopropanes examined. 26 references, 6 figures, 3 tables.

Gas phase ion chemistry of 2-fluoropropane by ion cyclotron resonance spectroscopy

The gas phase ion chemistry of 2-fluoropropane is reported. The parent ion fragments to yield (CH/sub 3/)/sub 2/CF/sup +/, CH/sub 3/CHF/sup +/, and CH/sub 2/CHF/sup +/ as the abundant primary ions, all of which react with the parent neutral by F/sup -/ transfer to yield (CH/sub 3/)/sub 2/CH/sup +/ (CH/sub 3/)/sub 2/CH/sup +/ in turn reacts with the parent neutral by H/sup -/ transfer to regenerate (CH/sub 3/)/sub 2/CF/sup +/, thus completing a chain reaction which leads to the conversion of 2-fluoropropane to a mixture of propane and 2,2-difluoropropane via ionic intermediates. This chain reaction is terminated by a slow condensation reaction of C/sub 3/H/sub 7//sup +/ with 2-fluoropropane to yield C/sub 6/H/sub 13//sup +/. A variety of trapped ion cyclotron resonance techniques, including in particular cyclotron resonance ion ejection methods, permits all of the rate constants for this reasonably complex reaction scheme to be extracted. 21 references, 2 figures, 3 tables.

Electron cyclotron resonance technique. X. Interactions of thermal-energy electrons with molecules of chlorine, hydrogen chloride, and methyl chloride

Electron cyclotron resonance technique. X. Interactions of thermal-energy electrons with molecules of chlorine, hydrogen chloride, and methyl chloride

Studies by the electron cyclotron resonance (ECR) technique: VIII. Interaction of low-energy electrons with the chlorine-containing molecules CCl 4, CHCl 3, CH 2Cl 2, C nH 2 n+1 Cl( n = 1 to 4). C 2H 3Cl, COCl 2, NOCl, CNCl and Cl 2

Rate constants, in some cases also activation energies and energy dependences, were measured for the capture of low-energy electrons by the molecules CCl 4, CHCl 3, CH 2Cl 2, C n H 2 n+1 Cl( n = 1 to 4), C 2H 3Cl, COCl 2, NOCl, CNCl and Cl 2 Potential energy curves were calculated for a number of negative ions. For ineffective scavengers the possibility of contributing scattering effects on the observed changes in signal intensity upon electron energy variation is indicated. In CCl 4 the observed energy dependence suggests the existence of intermediate negative ions. For Cl 2 good agreement was obtained between the calculated curves based on experimental data for electron capture and a recent self-consistent field analysis.

Ion-Molecule chemistry in formaldehyde by ion cyclotron resonance mass spectrometry

The ion—molecule reactions taking place in gaseous monomeric formaldehyde under electron impact have been studied by ion cyclotron resonance techniques. The main reaction product at low pressures is the secondary ion CH 3O +, which is formed by proton transfer from either of the two primary ions, CH 2O + or CHO +, to the neutral formaldehyde molecule. At higher pressures a number of proton transfer and hydrogen abstraction reactions are observed involving additional fragment ions producing secondary and tertiary ions, such as CH 4O + CH 5O +, CH 2 + and CH 3 +. At still higher pressures, product ions containing two carbon atoms are formed by complex reactions. The identity of all ions was verified by use of deuterium and 18O-labelled formaldehyde. Double resonance techniques were applied to confirm the reaction channel and to determine some of the reaction mechanisms. Relative rate constants of the main reactions were measured.

Photoionization and ion cyclotron resonance studies of the reaction of vibrationally excited C2H2+ ions with H2

The reaction C2H2++ H2 → C2H3+ + H has been studied using ion cyclotron resonance and photoionization mass spectrometric techniques. At thermal kinetic energies, the cross section for the reaction is near zero for ground state reactants but increases rapidly with increasing vibrational energy in the C2H2+ ions. The ratio of the cross sections for ions in the ν2 = 1 and ν2 = 2 states is approximately 1:2, respectively. Some reaction is observed at photoionization energies below the theshold for formation of ν2 = 1 ions owing to reaction of thermally excited ions and neutrals. For the distribution of vibrational energies in C2H2+ ions formed by electron impact at 15 eV, the rate constant for the reaction is 6.3±1.8×10−11 cm3/sec. Exchange of hydrogen atoms in nonreactive collisions between C2H2+ ions and D2 molecules has also been observed. An upper limit of Δ Hf(C2H3+)=267 kcal/mole is obtained.

Ion—molecule reactions in mixtures of hydrogen sulfide with ammonia and water

The ion chemistry of H 2SNH 3 and H 2SH 2O mixtures has been studied using ion cyclotron resonance techniques. The major bimolecular ion—molecule reactions occurring in each mixture have been identified, and the relative rate con- stants for reactions of the primary ions have been measured the cyclotron ejection method. Absolute rate constants have been determined from relative rates by reference to the rate constants for reactions occurring in the pure gases. A method has been devised for identifying parent—daughter relationships, and for measuring relative rate constants for reactions obscured by overlapping peaks in the mass spectrum.

Photodetachment of electrons from ethyl nitrene anion. An upper limit to the electron affinity of C 2H 5N·

N-nitrosodiethylamine has been found to be a good source of nitrogen containing anions, including C 2H 5N −. Photodetachment of electrons from C 2H 5N − has been studied with ion cyclotron resonance techniques. A threshold at 1.87 ± 0.16 eV can be taken as an upper limit to the electron affinity of ethyl nitrene.

Ion-Polar molecule collisions: the effect of ion size on ion-polar molecule rate constants; the parameterization of the average-dipole-orientation theory

Proton transfer rate constants from CH5+, C2H5+, C3H7+ and C4H9+ to NH3, CH3NH2, and (CH3)2NH have been measured at thermal energies by ion cyclotron resonance techniques. The data are compared with the predictions of the average-dipole-orientation theory. In all cases, the CH5+, C2H5+ and C3H7+ ions transfer a proton with essentially unit efficiency. The C4H9+ ions transfer protons with efficiencies between 0.6 and 0.9 depending on the substrate molecule. There is no evidence that the size of the ion has an appreciable effect on the magnitude of the proton transfer rate, at least within the accuracy of the ICR experiments. The average-dipole-orientation theory has been parameterized to permit determination of capture limit rate constants by reading a graph and making a simple calculation. A graph covering the range of polarizabilities and dipole moments of most molecules is included.

High-Frequency Cyclotron Resonance in Lead and the Electron-Phonon Interaction

The frequency and temperature dependences of the electron-phonon interaction have been investigated in lead by the Azbel'-Kaner cyclotron-resonance technique. The experiments have been performed in the unusual millimeter and submillimeter microwave band from 70 to 500 GHz, corresponding to the wavelength 4 to 0.6 mm. In this frequency band the photon energy value, $\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\le}2$ meV, is near the typical phonon energy in lead. The experiments were performed in the temperature range from 1.5 up to 6\ifmmode^\circ\else\textdegree\fi{}K. The effective mass ${m}^{*}$ and relaxation time $\ensuremath{\tau}$, measured on two different types of orbits, are frequency and temperature dependent. These dependences are directly related to the electron-phonon interaction. For both orbits ${m}^{*}$ is found to increase as the temperature squared and the frequency squared. The maximum relative increases are $\frac{{m}^{*}(5.4^{\ensuremath{\circ}}K)}{{m}^{*}(0^{\ensuremath{\circ}}K)}=1.03$ and $\frac{{m}^{*}(457 \mathrm{GHz})}{{m}^{*}(0 \mathrm{GHz})}=1.008$. The relaxation frequency ${\ensuremath{\tau}}^{\ensuremath{-}1}$ dependence varies as the cube of both the temperature and the frequency. The theoretical dependences on $T$ and $\ensuremath{\omega}$ are thus well confirmed, but the order of magnitude of the frequency effects is smaller than predicted.

Gas phase studies of N‐nitrosamines by ion cyclotron resonance spectroscopy

AbstractThe gas phase basicities of a series of cyclic and acyclic N‐nitrosamines were determined by ion cyclotron resonance techniques. The fragmentation pattern and ion‐molecule reactions of these compounds are discussed in terms of high resolution mass spectrometry and deuterium labeling. The presence of a unique rearrangement of the molecular ion is discussed in terms of specific ion‐molecule proton transfer reactions and fragment ion products.

Application of electron cyclotron resonance technique in studies of electron capture processes in the thermal energy range

Application of electron cyclotron resonance technique in studies of electron capture processes in the thermal energy range

Ion-molecule reactions in isotopic hydrogen by ion cyclotron resonance

Ion—molecule reactions of hydrogen, deuterium, and hydrogen deuteride ▪ and the crossed reactions ▪ have been studied using newly developed ion cyclotron resonance techniques. Thermal rate constants have been measured for these reactions which are generally in accord with previous experimental measurements and which are in excellent agreement with calculations based on simple Langevin polarization theory. Multiple resonance and multiple pulse techniques were used to evaluate isotope effects and effects of ion kinetic energy on these reactions. New reaction channels of dissociative proton transfer and charge transfer become open with increasing translational energy. These results are rationalized in part by statistical phase space theory and in part by simplified models involving orientation effects and separation of ceters of mass and charge in HD +.

Relative Rates and Their Dependence on Kinetic Energy for Ion–Molecule Reactions in Ammonia

Ion cyclotron resonance techniques are used to measure the relative rates and their dependence on kinetic energy for the major ion–molecule reactions in ammonia. Charge transfer is shown to compete with proton transfer in the reaction of both NH2+ and NH3+ with ammonia over an energy range from thermal velocities to 50 eV: NH4++NH2k1↗NH3++NH3k4↘NH3++NH3, NH4++NHk2↗NH2++NH3k3↘NH3++NH2. The rate for charge transfer increases with increasing kinetic energy while the rate for proton transfer decreases with kinetic energy. At thermal kinetic energies, k2 / k1 = 0.6 and k3 / k2 = 1.0. Resonant charge transfer from NH3+ was observed only for translationally excited ions.