Harry G. Hecht

Oxygen‐17 NMR Linewidths as Influenced by Proton Exchange in Water

Linewidths for the 17O nuclear magnetic resonance have been obtained at 29.0°±0.2°C in 10% H217O as a function of acidity with the sideband technique at 8 MHz. Computer methods have been used to solve the set of coupled linear equations from which line shapes as functions of the residence time and 2δ, the proton—17O spin—spin coupling constant, have been calculated. It has been possible to obtain a linear relationship between k1, the specific rate constant for the proton catalyzed exchange process, and 2δ. The spin—spin coupling constant has been redetermined by the acetone‐dilution procedure, and a value of 82±1 Hz has been obtained. Because of quadrupole relaxation of the 17O, the true coupling constant will be somewhat larger than the value obtained under these conditions of slow exchange. With the assumption of a value of 2δ of 580 rad sec−1, the acid and base catalyzed specific rate constants at 29.0°C are k1=8.2×109 mole−1 liter sec−1 and k2=4.6×109 mole−1 liter sec−1, respectively. However, it appe...

Interpretation of the absorption spectrum of single crystal UCl4

Temperature‐dependent polarized absorption spectra of single crystal UCl4 have been investigated in the range 4000–25 000 A. The spectra have been assigned and analyzed using the U4+ ion in a field of D2d point group symmetry as a model. An rms deviation of 91 cm−1 in the fit to 34 assigned levels was achieved using the following set of parameters: F2=172.6±1.8; F4=38.79±1.13; F6=2.565±0.101; ζ=1666±11; A 20〈 r2〉=−291.3± 82.6; A 40〈 r4〉=−378.4± 30.8; A 44〈 r4〉=−5940± 195; A 60〈 r6〉=−141.4± 30.3; A 64〈 r6〉=557.6± 184.6 (all units in cm−1). These optical data are interpreted to show that the ground state belongs to the Γ4 irreducible representation, with the first excited state being a Γ5 level at approximately 140 cm−1. The parameters are discussed in terms of the bonding characteristic of the coordinated complex ion.

A study of the kinetics of the reaction between H2 and F2 by EPR methods

Abstract Attesting to its interest for laser-related studies, the reaction between hydrogen and fluorine has recently been studied by a variety of experimental approaches in laboratories throughout the world. An EPR superheterodyne X-band spectrometer was used in the present work in conjunction with a fast flow gas mixing system to obtain both hydrogen and fluorine atom concentrations. The reactant hydrogen atoms were produced by the dissociation of molecular hydrogen in a 2450 MHz microwave discharge unit; the product fluorine atoms were produced by the reaction of hydrogen atoms with molecular fluorine. The changes in both atom concentrations were followed as fluorine was added incrementally to the helium-diluted reactants, H + H 2 . Values of the specific rate constants for the H + F 2 and F + H 2 reactions at 300°K have been found to be 2.5 ± 0.2 × 10 12 cm 3 mole −1 sec −1 and 4 ± 1 × 10 12 cm 3 mole −1 sec 1 , respectively. Under the conditions of our experiments, i.e., at pressures of ca. 2 Torr and with quartz flow tube walls coated with boric acid, the contribution of a branched-chain step to the reaction mechanism appears to be minimal.

Study of the Structure of Nickel in Soda—Boric Oxide Glasses

The results of an investigation of the structure of Ni+ +, ions in Na2O–B2O3 glasses by optical and EPR techniques are reported. The coordination about the ion sites is found to be octahedral, and a small amount of covalency is inferred. The crystal‐field splitting of the d8 levels decreases as the Na2O content of the glass increases. No direct evidence for the boric oxide anomaly was found.

Low temperature magnetic susceptibility of UCl4

The magnetic susceptibility of powdered UCl4(s) has been measured in the temperature range 4–300 °K using the Faraday method. The data are qualitatively consistent with our previous analysis of the optical spectrum, but suggest that the first excited Γ5 level should lie at approximately 110 cm−1 above the ground state.

A single crystal ESR study of the Cu(C5H5N)42+ ion in Cd(C5H5N)4S2O8

Abstract The ESR spectra of Cu(C 5 H 5 N) 4 2+ in single crystals of Cd(C 5 H 5 N) 4 S 2 O 8 are reported and analyzed. It is found that the ESR parameters are consistent with an essentially square planar configuration, and the orientation of the ions in the crystal is determined. Using powder reflectance techniques, the optical transition energies are inferred and used in a molecular orbital treatment. The assignment of optical transitions determined in this study is compared with that reported by other workers, and the m. o. parameters are derived.

NMR Study of Na3UF8 Structure and Hyperfine Effects

Nuclear magnetic resonance spectra of polycrystalline Na3UF8 were studied experimentally. The magnetic field dependence of the 19F second moment allowed a separation of its field‐dependent and field‐independent parts. The temperature dependence of the field‐independent part exhibits no discontinuities attributable to phase transitions and only a slow transition at about 250°K attributed to hindered molecular rotation of the isolated UF8 units. The temperature dependence of the field‐dependent part also exhibits no discontinuities. It does reflect the paramagnetic susceptibility which obeys, to within the accuracy of the experiment, the Curie law. The isotropic chemical shift is small, i.e., − 0.07% ± 0.01% with respect to F2 at 292°K and − 0.11% ± 0.01% at 175°K. The even smaller chemical‐shift anisotropy is approximately 25% of the isotropic shift. These shift data are consistent with a system containing one 5f electron as the unpaired spin. The 19F spectra and the temperature dependence of the field‐dep...