Henry Zeldes

Paramagnetic Resonance Study of Liquids during Photolysis: Hydrogen Peroxide and Alcohols

Paramagnetic resonance spectra of free radicals in liquids have been studied during the course of intense irradiation with ultraviolet light. Equipment is described in which the liquid sample flows through the microwave cavity of the spectrometer and is photolyzed as it passes the sensitive region of the cavity. In this way the steady‐state concentration of short‐lived radicals have been observed. Temperatures from about −70° to 60°C have been used. A number of alcohols containing up to 1% H2O2 have been studied. In the absence of dissolved oxygen the main products are the radicals formed by abstraction of a hydrogen from the position alpha to the hydroxyl group. The radicals RĊHOH where R is H, CH3, C2H5, C3H7, (CH3)2CH, and C6H5 have values of aα near room temperature ranging from 14.7 to 17.4 G and g values ranging from 2.00298 to 2.00334. Those radicals with beta hydrogens have values of aβ ranging from 20.0 to 22.2 G. The ring protons of C6H5ĊHOH are inequivalent. When the alpha hydrogen is abstracte...

A Paramagnetic Species in Irradiated NaNO2

Single crystals of sodium nitrite were irradiated with Co60 gamma rays at 77°K and studied by the paramagnetic resonance method. An anisotropic three‐line hyperfine spectrum associated with a single paramagnetic species was observed. The hyperfine structure arises from a nitrogen nucleus in the paramagnetic species at a position of mm point symmetry. The principal values of the g tensor and the hyperfine tensor were deduced as well as the directions of their principal axes. The paramagnetic species is believed to be NO2.

Paramagnetic Resonance Study of Liquids during Photolysis. II. Acetone and Solutions Containing Acetone

Paramagnetic resonance spectra in liquid acetone and acetone solutions were studied during the course of intense irradiation with ultraviolet light. In the presence of RH, an alcohol or ether, which served as a good hydrogen donor, both radicals of the reaction CH3COCH3+RH→(CH3)2COH+R were seen. The abstracted H atom was taken from the carbon alpha to the O atom of the alcohol or ether. When pure liquid acetone was photolyzed, both radicals of the reaction CH3COCH3+CH3COCH3→(CH3)2COH+CH2COCH3 were seen. In addition some ĊH3 was seen. Higher concentrations of ĊH2COCH3 and ĊH3 were produced by photolyzing acetone containing 1% H2O2. In the latter case, it is believed that the radical OH was produced from the H2O2. The OH radical then abstracted an H atom from acetone to give ĊH2COCH3. It is thought that ĊH3 resulted from the reaction CH2COCH3→H2C=C=O+CH3. Accurate measurements were made of the g values and hyperfine parameters for (CH3)2ĊOH, ĊH2OH, and CH3ĊHOH in both water‐rich and acetone‐rich solutio...

Paramagnetic Resonance Study of Irradiated Single Crystals of Calcium Tungstate

Gamma irradiation of calcium tungstate at 77°K produces two paramagnetic species in high yield. Measurements of yields and of rates of disappearance upon warming indicate the two species are formed and disappear upon warming in one to one correspondence. The principal axis directions and g tensors have been measured and indicate that one species contains a surplus electron while the other is electron‐deficient (hole). Hyperfine effects of W183 have been observed. The electron‐deficient species contains two tungsten atoms with small isotropic hyperfine interactions. Its unpaired electron must be highly localized in orbitals of atoms other than tungsten. The electron‐surplus species contains one tungsten atom with an anisotropic hyperfine interaction. This center could be WO43—, but from the lack of symmetry of the measured g values it must be formed near a lattice defect. Experiments with heat‐treated crystals indicate lattice defects to be important in the radiation effect.

Ground‐State Splitting of Trivalent Gd and Cm in ZrSiO4, HfSiO4, and ThSiO4, Determined by ESR

The electron spin resonance spectrum of trivalent gadolinium impurity in the tetragonal host crystals of ZrSiO4, ThSiO4, and HfSiO4 has been observed at X band, and the spin‐Hamiltonian parameters were obtained at various temperatures. The dominant second‐order parameter B20 for Gd was observed to be negative in all three crystals. Hyperfine structure for the odd isotopes 155Gd and 157Gd was clearly resolved and measured. In ThSiO4 crystals doped with trivalent curium, no ESR signals were detected, supporting the assumption of a large negative B20 term for this ion in these hosts.

Common Error Made in Treating Hyperfine Effects in Electron Paramagnetic Resonance Studies of Free Radicals

Expressions are presented for the case of a single electron (or hole) in a completely quenched orbital (isotropic g factor) which has an axis of symmetry. Expressions are given for the case of a hybridized s-p orbital and it is shown that the angular dependence of the hyperfine splitting In the absence of s contributions is (3 cos/sup 2/ theta + l)1/2. (C.J.G.)

Zeeman Effect on the Quadrupole Spectra of Sodium, Potassium, and Barium Chlorates

All features of the Zeeman pattern of NaClO3 that were examined can be deduced from the crystal symmetry and knowledge of the orientation of the crystal axes in the magnetic field. The crystal axes could be located with respect to the magnet goniometer to within 0.05° by observation of the Zeeman pattern. The line width was found to be 1.2 kc between flexes. A method was devised for orienting KClO3 and Ba(ClO3)2·H2O crystals by attaching a NaClO3 crystal and observing its Zeeman pattern. In KClO3, the field gradient tensor asymmetry parameter η was found to be about 0.006 and the z‐principal axis was located and compared with features of the structure. The line, one of the sharpest yet observed, measured 0.29 kc between flexes. In Ba(ClO3)2·H2O, the upper limit for η was found to be 0.05. The z‐principal axes were located and compared with features of the crystal structure. The line width was found to be about 3 kc.

Zeeman Effect on the Quadrupole Spectrum of Iodic Acid

The pure quadrupole spectrum of I127 in iodic acid has been observed at several temperatures. At 22°C the z component of the quadrupole coupling is 1126.9 Mc and η, the asymmetry parameter is 0.4505. Zeeman studies on the low frequency transition (±1/2→±3/2) showed an intensity effect that depended on the orientation of the crystal in the rf coil. Extra Zeeman components were present that resulted from a proton interaction, and the study of these essentially located the hydrogen in the crystal lattice. Zeeman studies on the high frequency transition (±3/2→±5/2) showed four components for each type of iodine atom, the two not normally present unless η is large were weak. The splittings of the levels were uniquely assigned and the directions of the principal axes computed.

Paramagnetic Resonance Study of Liquids during Photolysis. VIII. An Emission Spectrum from Solutions of Tartaric Acid

Paramagnetic resonance spectra of several free radicals were observed during photolysis of concentrated aqueous solutions of tartaric acid. Radical A, identified as HOOCCH(OH)CH(OH), gives a spectrum of eight hyperfine lines all of which are in emission. This radical is converted by a pinacollike rearrangement to HOOCĊHCHO, the spectrum of which was also observed. The chemical lifetime and relaxation time of radical A are discussed. By progressively increasing the pH of the solution, the chemical lifetime is lengthened and the emission spectrum is progressively transformed to an absorption spectrum. At intermediate stages, intensity anomalies are seen and discussed. Other radicals seen in this system are also discussed.

Paramagnetic Resonance Study of Liquids during Photolysis. IV. Free Radicals from Acetaldehyde, Diacetyl, and Acetoin

Paramagnetic resonance spectra in solutions at room temperature were studied during irradiation with ultraviolet light. The radical CH3ĊOHCOCH3, the acetoin radical, was produced from diacetyl in the presence of good H‐atom donors. Using p‐dioxane as the donor, the radical produced from the donor was also seen. The acetoin radical and CH3ĊHOH were produced from acetaldehyde in the absence of a good H donor. By adding a good donor to acetaldehyde solutions, the yield of the acetoin radical was suppressed, and the radical produced from the H‐atom donor appeared. Reasonable reactions are proposed. In nearly neutral aqueous solutions or in slightly alkaline isopropyl alcohol solution, the acetoin radical was converted to the anion CH3COCOCH3−. The parameters of the acetoin radical and of its anion were measured in a number of solutions. The radical CH3ĊHOH was produced from acetoin in a variety of solutions, showing that cleavage of the acetoin molecules takes place. The spectrum of the acetoin radical underw...