Daniel D. Elleman

Thermal energy charge transfer reactions of rare-gas ions to methane, ethane, propane, and silane - The importance of Franck-Condon factors.

Abstract Thermal energy charge transfer rate constants from He+, Ne+, Ar+, Kr+ and XE+ to CH4, CD4, C2H6, C3H8 and SiH4 have been measured using ion-cyclotron resonance spectroscopy. The data are interpreted in terms of a model that presumes the magnitude of the rate constant is directly related to the magnitude of the Franck-Condon factor connecting the molecular neutral and ion. Addition measurement between N2O+, CO+2, CO+ and N+2 charge trans ferring to SiH4 indicate the ion-neutral collision distorts the Franck-Condon manifold from that appropriate to sudden ionization processes (photon or electron impact).

Analysis of the Ion–Molecule Reactions in Gaseous H2, D2, and HD by Ion Cyclotron Resonance Techniques

Using recently developed ion cyclotron resonance (ICR) techniques, the thermal-energy rate constants of the reactions H2++H2→H3++H, D2++D2→D3++D, H2D++D↗HD++HD↘HD2++H, have been measured. The values of k1 = 2.11, k2 = 1.60, k3a = 0.75, and k3b = 1.05 × 10−9cc molecule−1·sec−1 are in good agreement with the predictions of the Langevin theory and agree in general with other data where available. The energy dependencies of (R1)–(R3) were studied by a variety of double-resonance techniques. An analysis of the energy dependence implies that a dual reaction mechanism is operative in (R1)–(R3). At low energies (KE < 1 eV) both a complex formation and a stripping mechanism occur while at higher energies the stripping mechanism becomes dominant. The relative energy dependencies of (R3a) and (R3b) are interesting in that the ratio [H2D+]/[HD2+] considerably increases as the reactant-ion energy increases (at low energies). The implication is that as the stripping mechanism becomes more dominant the importance of the...

An NMR Study of Indene Using a Proton‐Proton Decoupling Technique

The 60 Mc/sec high‐resolution NMR spectrum of the protons of the five‐membered ring of indene [Complex chemical formula] has been studied with the aid of the audio sideband phase detection proton—proton spin decoupling technique. The chemical shifts and the spin—spin coupling constants have been measured. The relative sign of the spin coupling constant JAX was determined to be different than that of JAK and JKX by double irradiation experiments. Certain long‐range couplings of the aromatic protons with the five‐membered ring protons were detected.

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.

Development of an electrostatic positioner for space material processing

This paper describes an electrostatic positioning instrument which was developed at the Jet Propulsion Laboratory to enable experimenters to conduct containerless material science experiments in space. Samples that are to be studied are electrically charged and controlled by the electrostatic force produced by a set of properly arranged electrodes. Three different types of positioners are described, i.e., the dish type, the ring type, and the tetrahedral type. In all these systems, the positioning and the damping of the sample is accomplished by a feedback control system. The advantage of this electrostatic positioning method, in comparison to the other methods, such as acoustic and electromagnetic, lies in the fact that it can operate in a high vacuum and does not require the material to be electrically conductive as long as the material can carry a certain amount of charge.

Proton NMR Spectra of Cyclopentadiene, 1,3‐Cyclohexadiene, 1,3‐Cyclooctadiene, and 1,2‐Dihydronaphthalene

The proton NMR coupling constants between vinyl protons in cyclopentadiene (I), 1,3‐cyclohexadiene (II), and 1,3‐cyclooctadiene (III) have been obtained by analyses of the spectra of the latter protons when the methylene protons were decoupled. An analysis of the full spectrum of I has also been achieved. Analysis of the spectrum of 1,2‐dihydronaphthalene (IV) was undertaken both to obtain a value of 3JHH across the olefinic double bond, and to compare certain of its coupling constants with those from our previous work on indene. The long‐range coupling constants between vinyl protons in the planar molecule I and nearly planar II are significantly different from those in the nonplanar III. The differences are discussed in terms of the conformations of these molecules, and the importance of these results for testing theories of long‐range coupling constants is pointed out.

Kinetic Analysis of the Concurrent Ion–Molecule Reactions in Mixtures of Argon and Nitrogen with H2, D2, and HD Utilizing Ion‐Ejection–Ion‐Cyclotron‐Resonance Techniques

A technique is developed for using the ion‐ejection mode of ion‐cyclotron‐resonance spectroscopy for determining quantitative ion–molecule rate constants in concurrent reaction systems. Rate constants for the reaction of H2+, D2+, HD+, H3+, and D3+ with Ar and N2 are reported along with the concurrent reactions of Ar+ and N2+ with H2, D2, and HD. The results are discussed and compared with the Gioumousis and Stevenson theory and other experimental data where available. The energy dependence of the various reactions are reported as determined by double‐resonance experiments. The results are discussed in terms of the phase‐space theory of Light. Indications of the mechanism of reaction (complex formation or stripping) were made where appropriate and compared with the crossed‐beam data.

19F Chemical Shift Tensor in Group II Difluorides

The multiple pulse nuclear magnetic resonance techniques have been used to measure the 19F chemical shift, or nuclear magnetic shielding, tensor in a series of Group II difluorides. For the cubic difluorides measured values relative to a C6F6 reference are: CaF2, −61 ppm; SrF2, −82; BaF2, −154 ppm; CdF2, +33 ppm; and HgF2, +32 ppm. For the two noncubic difluorides principal values of the chemical shift tensors relative to C6F6 are; for MgF2, +13, +28, and +43 ppm; and for ZnF2, +15, +38, and +59 ppm. The chemical shifts from the cubic difluorides were found to correlate well with electronegativities and a covalency parameter calculated from electron spin resonance superhyperfine interaction parameters. A theoretical calculation of the chemical shift tensor for MgF2 is presented and give good agreement with the experimental data, accounting for 90% of the chemical shift anisotropy.

Relative Signs of the Nuclear Spin Coupling Constants in Propylene Oxide and Indene Oxide

The 60‐Mc/sec high‐resolution NMR spectrum of propylene oxide was analyzed as an ABCD3 nuclear spin system in the conventional iterative manner utilizing in addition double resonance to decouple the D3 (methyl group) protons from the ABC protons. A fit was obtained by two sets of parameters whose main difference was that either both long‐range couplings JBD and JCD are positive with respect to the other couplings or only JCD is negative. By use of a weak perturbing rf field to irradiate a particular resonance transition it was determined that JCD has a different sign than the other couplings.The 60‐Mc/sec spectrum of the protons of the five‐membered ring of indene oxide (II) was analyzed as an ABCD system with the aid of triple‐irradiation experiments in which the long‐range couplings of the A, C, and D protons with the aromatic ring protons were destroyed by a large rf irradiation applied at the resonance position of the aromatic protons while a second weaker perturbing irradiation was applied at particu...

Proton anisotropic chemical shift spectra in a single crystal of hexagonal ice

The proton anisotropic chemical shift spectra in a single crystal of hexagonal ice are reported for the first time. (AIP)