Robert G. Hayes

Nuclear magnetic resonance studies of the interaction of water with the polar region of phosphatidylcholine micelles in benzene

1. 1. Both the hydrocarbon chains and the trimethylammonium groups of phosphatidylcholine micelles in benzene have more motional freedom than can be explained by micellar rotation. 2. 2. Addition of water, which is solubilized within the micelles, slows the motion of the hydrocarbon chains but increases the motion of the trimethylammonium groups. 3. 3. The hydrocarbon and the trimethylammonium proton linewidths have a weak temperature dependence, suggesting that the motions of these groups is not an activated process, but may be described by a local viscosity. 4. 4. 2H2O is much less efficient than H2O in influencing the trimethylammonium proton linewidth, suggesting that the interaction between the water and the micelles is dominated by hydrogen bonding rather than by electrostatic interactions.

Paramagnetic Resonance of Alkyl Radicals from Dissociative Electron Attachment in γ‐Irradiated Organic Glass

The radicals CH3·, CH3CH2·, CH3CH2CH2·, (CH3)3C·, (CH3)3CCH2·, and C6H5ĊHCH3 have been identified by EPR in γ‐irradiated dilute solutions of the corresponding halides in 3‐methylpentane at 77°K. For 0.4 mole % CH3I, G(CH3·)=1.2. Methyl radicals disappear by some first‐order rate process for which k=4.6×10−4 sec−1. Other radicals did not decay measurably under similar conditions. The results are consistent with the mechanism of dissociative thermal electron attachment, RX+e−→R·+X−, which is an efficient, selective process whenever the electron affinity of X exceeds the bond dissociation energy of R—X.

Electron Paramagnetic Resonance Studies of Mn(CN)5NO2− and Cr(CN)5NO3− in Dilute Single Crystals

We have studied the electron paramagnetic resonance spectra of Mn(CN)5NO2− and Cr(CN)5NO3− as dilute solutions in single crystals of various diamagnetic hosts. From these measurements, we have obtained the spectroscopic splitting factor tensor and the hyperfine tensors to the central metal atom and nitrosyl nitrogen. In the case of Cr(CN)5NO3−, we have also measured the hyperfine tensor to carbon‐13 in the equatorial and axial cyanides. We have measured the quadrupole coupling constant to 55Mn in Mn(CN)5NO2−. We have attempted to construct a coherent picture of the electronic structure of the complexes from these data. This attempt has been only partly usccessful, primarily because the spectroscopic splitting factors are much nearer the free spin value than one expects on the basis of the hyperfine data.

Nonadiabatic Effects in the Internal Rotation of ·CH2COO− in Irradiated Zinc Acetate Dihydrate

The EPR spectrum of the ·CH2COO− radical in a single crystal host displays nonadiabatic motional effects. A phenomenological theory is suggested, based on the density matrix of the spin system, and a technique is described for rapid calculation of simulated spectra.

Microwave Spectrum of Methyl Difluoramine : Structure, Conformation, Dipole Moment, Barrier to Internal Rotation, and Quadrupole Coupling Constants of the Molecule

The microwave spectra of the common and three isotopic species of methyl difluoramine have been investigated from 8 to 27 Gc/sec. From an analysis of the rotational constants the following structural parameters are obtained: DCN1.449 ACH1.091 ANF1.413 A∠NCHs110∘22′∠FNF100∘59′∠NCHa106∘14′∠CNF104∘38′∠HsCHa111∘45′∠HaCHa110∘15′. The conformation of the methyl group is such that the in‐plane CH bond (CHs) is staggered with respect to the NF bonds. The methyl group is nearly symmetric and the NCH angles indicate the methyl group and its symmetry axis to be tilted away from the CN bond axis and towards the unshared electron pair by about 2.8°. Quadrupole hyperfine structure was resolved and analyzed for each of the four species. The quadrupole coupling constants of the common species are: χAA=6.45 Mc/sec, χBB=0.46 Mc/sec, χCC=−6.91 Mc/sec. A crude estimate of χBC (2.8±0.6 Mc/sec) is obtained by comparing data for the common and symmetric monodeutero species. The rotation of principal axes in going from one speci...

EPR Studies of Mo(CN)5NO3−: Magnetic Parameters and Analysis of the Ligand Hyperfine Structure

We have observed the EPR spectrum of the ion Mo(CN)5NO3− under various conditions and have satisfied ourselves that the given formulation is correct. Our best set of magnetic parameters, for the ion in K3Co(CN)6, is: g∥=1.9736, g⊥=2.0168, A∥(Mo)=163.2 Mc/sec, A⊥=76.4 Mc/sec. We have observed an extensive ligand hyperfine structure at 77°K, which we have assigned to 14N in the nitrosyl and in the equatorial cyanides. We find the 14NO hyperfine tensor to have axial symmetry about the figure axis of the complex, with principal values A∥=3.81 Mc/sec, A⊥=11.30 Mc/sec. We find the C14N hyperfine tensor to have approximate axial symmetry about an axis perpendicular to both the figure axis of the complex and the Mo–C–N bond axis, with principal values A∥=+6.62 Mc/sec, A⊥=−1 Mc/sec. We thus find the fraction of unpaired electron delocalized onto the nitrogen of each cyanide to be 0.053.

Studies of tetra‐(p‐fluorophenyl)porphyrins by x‐ray photoelectron spectroscopy: Effect of reduction on charge distribution in Fe compounds

We have studied the x‐ray photoelectron spectra arising from nitrogen 1s, fluorine 1s, and metal 2p levels of several compounds of tetra‐ (p‐fluorophenyl)porphine, including the free base and several iron compounds. Using the fluorine 1s level as an internal calibrant, we find that the N 1s binding energies agree well with previous results from this laboratory. The difference in Fe 2p binding energy between Fe(II) and low‐spin Fe(III) compounds is 1.6 eV. We show that the difference in the charge on Fe between the two types of compounds is equal to some 0.09 electron charges. Satellite structure, observed adjacent to the N 1s photolines, is also discussed.

Mass spectra and bond energies of lanthanide tricyclopentadienyl complexes

Abstract Ionization potentials and appearance potentials for Cp3Nd, Cp3Sm, Cp3Yb, and Cp2Yb are reported. Using this information, the first bond dissociation energy of Cp3Yb is calculated to be 58 ± 5 kcal. Also, fragmentation patterns of these compounds are discussed in relationship to the type of bonding involved.

Evidence from x-ray photoelectron spectroscopy on the charge distribution in various chromium compounds

Measurements of various core-level binding energies in the compounds K3CrF6, K3Cr(CN)6 and Cr(acac)3 are reported. The binding energies of the LIII level of Cr in these compounds, and in Cr(CO)6 and K2CrO4, are analyzed to yield charge differences between the chromium atom in Cr(acac)3 and in the other compounds.

5 – THERMALLY INDUCED CHANGES IN THE STABLE CARBON AND NITROGEN ISOTOPE RATIOS OF CHARRED BONES

Publisher Summary Cremations, whether accidental or deliberate, are difficult to work with because they are usually fragmentary. However, cremation is rarely complete, and cremated burials often provide bone fragments suitable for many types of osteological investigations. Morphological analyses of cremated bones can provide information about sex, age, health, and cause of death. It is often assumed that cremation produces highly oxidized bone fragments that are little more than inorganic ash, but this is not the case for most prehistoric cremations. Bone fragments often display a gradient of thermal alteration, ranging from calcined through blackened to apparently unaltered, sometimes even on the same bone. Burned bones can also be subjected to chemical studies, although these are rarely done. Many cremations produce bones that still contain organic matter in the form of thermally altered organics or reduced carbon. This is especially true for prehistoric cremations, where the large amount of fuel necessary for a total cremation may not have been readily available to nonindustrial societies. In many cases, charred bones from archaeological contexts can be expected to contain more organic carbon than uncharred bones from the same context, because reduced carbon in charred bone is more resistant to diagenetic change than uncharred collagen and other organic fractions of bone. Cremated burials would provide an abundant and promising source of paleodietary data through isotope studies if correct techniques were available.